docs: List private headers for gtk-doc to ignore

We have a lot of private headers that should not be used by gtk-doc when
scanning for symbols.

docs/reference/gtk/meson.build

 private_headers = [
+  'gdkpixbufutilsprivate.h',
+  'gtkaccelgroupprivate.h',
+  'gtkaccelmapprivate.h',
+  'gtkactionhelperprivate.h',
+  'gtkactionmuxerprivate.h',
+  'gtkadjustmentprivate.h',
+  'gtkallocatedbitmaskprivate.h',
+  'gtkappchooserprivate.h',
+  'gtkapplicationaccelsprivate.h',
+  'gtkapplicationprivate.h',
+  'gtkbindingsprivate.h',
+  'gtkbitmaskprivate.h',
+  'gtkboxprivate.h',
+  'gtkbuilderprivate.h',
+  'gtkbuttonprivate.h',
+  'gtkcellareaboxcontextprivate.h',
+  'gtkcheckbuttonprivate.h',
+  'gtkcheckmenuitemprivate.h',
+  'gtkcolorchooserprivate.h',
+  'gtkcoloreditorprivate.h',
+  'gtkcolorplaneprivate.h',
+  'gtkcolorscaleprivate.h',
+  'gtkcolorswatchprivate.h',
+  'gtkcomboboxprivate.h',
+  'gtkcontainerprivate.h',
+  'gtkcssanimatedstyleprivate.h',
+  'gtkcssanimationprivate.h',
+  'gtkcssarrayvalueprivate.h',
+  'gtkcssbgsizevalueprivate.h',
+  'gtkcssbordervalueprivate.h',
+  'gtkcsscalcvalueprivate.h',
+  'gtkcsscolorvalueprivate.h',
+  'gtkcsscornervalueprivate.h',
+  'gtkcssdimensionvalueprivate.h',
+  'gtkcssdynamicprivate.h',
+  'gtkcsseasevalueprivate.h',
+  'gtkcssenumvalueprivate.h',
+  'gtkcssfiltervalueprivate.h',
+  'gtkcssfontfeaturesvalueprivate.h',
+  'gtkcssfontvariationsvalueprivate.h',
+  'gtkcssiconthemevalueprivate.h',
+  'gtkcssimagebuiltinprivate.h',
+  'gtkcssimagecrossfadeprivate.h',
+  'gtkcssimagefallbackprivate.h',
+  'gtkcssimageiconthemeprivate.h',
+  'gtkcssimageinvalidprivate.h',
+  'gtkcssimagelinearprivate.h',
+  'gtkcssimagepaintableprivate.h',
+  'gtkcssimageprivate.h',
+  'gtkcssimageradialprivate.h',
+  'gtkcssimagerecolorprivate.h',
+  'gtkcssimagescaledprivate.h',
+  'gtkcssimageurlprivate.h',
+  'gtkcssimagevalueprivate.h',
+  'gtkcssimagewin32private.h',
+  'gtkcssinheritvalueprivate.h',
+  'gtkcssinitialvalueprivate.h',
+  'gtkcsskeyframesprivate.h',
+  'gtkcsslookupprivate.h',
+  'gtkcssmatcherprivate.h',
+  'gtkcssnodedeclarationprivate.h',
+  'gtkcssnodeprivate.h',
+  'gtkcssnodestylecacheprivate.h',
+  'gtkcssnumbervalueprivate.h',
+  'gtkcsspalettevalueprivate.h',
+  'gtkcssparserprivate.h',
+  'gtkcsspathnodeprivate.h',
+  'gtkcsspositionvalueprivate.h',
+  'gtkcssproviderprivate.h',
+  'gtkcssrepeatvalueprivate.h',
+  'gtkcssrgbavalueprivate.h',
+  'gtkcsssectionprivate.h',
+  'gtkcssselectorprivate.h',
+  'gtkcssshadowsvalueprivate.h',
+  'gtkcssshadowvalueprivate.h',
+  'gtkcssshorthandpropertyprivate.h',
+  'gtkcssstaticstyleprivate.h',
+  'gtkcssstringvalueprivate.h',
+  'gtkcssstylechangeprivate.h',
+  'gtkcssstyleprivate.h',
+  'gtkcssstylepropertyprivate.h',
+  'gtkcsstransformvalueprivate.h',
+  'gtkcsstransientnodeprivate.h',
+  'gtkcsstransitionprivate.h',
+  'gtkcsstypesprivate.h',
+  'gtkcssunsetvalueprivate.h',
+  'gtkcssvalueprivate.h',
+  'gtkcsswidgetnodeprivate.h',
+  'gtkcsswin32sizevalueprivate.h',
+  'gtkdialogprivate.h',
+  'gtkdndprivate.h',
+  'gtkentryprivate.h',
+  'gtkeventcontrollerlegacyprivate.h',
+  'gtkeventcontrollerprivate.h',
+  'gtkfilechoosererrorstackprivate.h',
+  'gtkfilechoosernativeprivate.h',
+  'gtkfilechooserprivate.h',
+  'gtkfilechooserwidgetprivate.h',
+  'gtkfilefilterprivate.h',
+  'gtkfontchooserprivate.h',
+  'gtkfontchooserwidgetprivate.h',
+  'gtkgesturedragprivate.h',
+  'gtkgesturelongpressprivate.h',
+  'gtkgesturemultipressprivate.h',
+  'gtkgesturepanprivate.h',
+  'gtkgestureprivate.h',
+  'gtkgesturerotateprivate.h',
+  'gtkgesturesingleprivate.h',
+  'gtkgesturestylusprivate.h',
+  'gtkgestureswipeprivate.h',
+  'gtkgesturezoomprivate.h',
+  'gtkgizmoprivate.h',
+  'gtkheaderbarprivate.h',
+  'gtkhslaprivate.h',
+  'gtkiconcacheprivate.h',
+  'gtkiconcachevalidatorprivate.h',
+  'gtkiconhelperprivate.h',
+  'gtkiconprivate.h',
+  'gtkiconthemeprivate.h',
+  'gtkiconviewprivate.h',
+  'gtkimagedefinitionprivate.h',
+  'gtkimageprivate.h',
+  'gtkimcontextsimpleprivate.h',
+  'gtkimmoduleprivate.h',
+  'gtkkineticscrollingprivate.h',
+  'gtklabelprivate.h',
+  'gtklockbuttonprivate.h',
+  'gtkmagnifierprivate.h',
+  'gtkmediafileprivate.h',
+  'gtkmenubuttonprivate.h',
+  'gtkmenuitemprivate.h',
+  'gtkmenuprivate.h',
+  'gtkmenushellprivate.h',
+  'gtkmodulesprivate.h',
+  'gtkmountoperationprivate.h',
+  'gtknativedialogprivate.h',
+  'gtknomediafileprivate.h',
+  'gtkorientableprivate.h',
+  'gtkplacessidebarprivate.h',
+  'gtkplacesviewprivate.h',
+  'gtkplacesviewrowprivate.h',
+  'gtkpointerfocusprivate.h',
+  'gtkpopoverprivate.h',
+  'gtkprinter-private.h',
+  'gtkprintoperation-private.h',
+  'gtkprivate.h',
+  'gtkprogresstrackerprivate.h',
+  'gtkrangeprivate.h',
+  'gtkrbtreeprivate.h',
+  'gtkrenderbackgroundprivate.h',
+  'gtkrenderborderprivate.h',
+  'gtkrendericonprivate.h',
+  'gtkrendernodepaintableprivate.h',
+  'gtkroundedboxprivate.h',
+  'gtkscalerprivate.h',
+  'gtksearchentryprivate.h',
+  'gtkselectionprivate.h',
+  'gtksettingsprivate.h',
+  'gtkshortcutsshortcutprivate.h',
+  'gtkshortcutswindowprivate.h',
+  'gtksidebarrowprivate.h',
+  'gtksizegroup-private.h',
+  'gtksizerequestcacheprivate.h',
+  'gtksnapshotprivate.h',
+  'gtkstyleanimationprivate.h',
+  'gtkstylecascadeprivate.h',
+  'gtkstylecontextprivate.h',
+  'gtkstylepropertyprivate.h',
+  'gtkstyleproviderprivate.h',
+  'gtktextbufferprivate.h',
+  'gtktextchildprivate.h',
+  'gtktextdisplayprivate.h',
+  'gtktexthandleprivate.h',
+  'gtktextiterprivate.h',
+  'gtktextlayoutprivate.h',
+  'gtktextmarkprivate.h',
+  'gtktexttagprivate.h',
+  'gtktextviewprivate.h',
+  'gtktogglebuttonprivate.h',
+  'gtktoolbarprivate.h',
+  'gtktooltipprivate.h',
+  'gtktooltipwindowprivate.h',
+  'gtktreeprivate.h',
+  'gtkutilsprivate.h',
+  'gtkwidgetpaintableprivate.h',
+  'gtkwidgetpathprivate.h',
+  'gtkwidgetprivate.h',
+  'gtkwin32drawprivate.h',
+  'gtkwin32themeprivate.h',
+  'gtkwindowprivate.h',
+  'gtk-text-input-client-protocol.h',
 ]
 
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