and simplify gimp_draw_tool_on_vectors()'s API.

1:1 copies of the same functions in gimpdrawtool.[ch].

Bump librsvg requirement to 2.40.6.
This was bug 620923 in librsvg, fixed from 2.40.6 as of commit
5ba4343bccc7e1765f38f87490b3d6a3a500fde1 in their master branch.

And regenerate AUTHORS.

and api to call them. Not used anywhere yet.

it was already working perfectly, but it's so simple I'd like to make
it "perfect" as a GimpToolWidget implementation example.

build-export is actually a low-level tool used by flatpak-builder. When
using it directly, debug and locale extensions were not extracted as
separate extensions (unless tweaking complicated command lines), ending
up with a huge GIMP flatpak with the current procedure.
Since flatpak 0.9.5, the option --export-only has been added to
`flatpak-builder` so that the build and the export can be made in 2
separate steps while using the high level procedure.
See: https://github.com/flatpak/flatpak/issues/824

which is the code that calculates handle size based on pointer
proximity. Use the new function in GimpToolHandleGrid and
GimpToolLine, and clean up some stuff in GimpToolLine.

Current comment was implying that PDF had some kind of fixed PPI, or
that a 72 PPI was hardcoded in cairo. This is not at all what this is
about. Cairo simply has a concept of user-space coordinates, and from
what I gather, it seems that this is set as "point", the typographical
unit of measure (not as a screen point). In such context, cairo_scale()
is used to update the transformation matrix (which will transform from
user to device units, i.e. pixels) so that we can draw with pixels. In
other words, both the user and device units will be pixels in subsequent
calls.
It turns out that 1 inch == 72 points. This is not a PPI/DPI at all and
the comment was completely misleading.

No need to loop through layers, which may be wrong anyway with
layers-as-pages. Also we were using the layer sizes without even
checking their offsets yet filling from (0, 0). This code was flawed in
many aspects.

- add utility function gimp_transform_tool_get_widget()
- reorder some functions
- cleanup in draw()

using g_object_bind_property().

Simply use g_object_bind_property() to connect the grid properties of
GimpTransformOoptions and GimpToolTransformGrid and remove all other
grid property setting code.

It seems proper enough now.

and fix a few glitches from tool widget porting.

Added a "Reverse Order" option when "Layers as pages" is checked.
"Layers as pages" option is greyed out if the image has only 1 layer.

and clean up and reorder the code quite a bit.

The same values as in gimpdrawtool.h, tool widgets in display/ must
not include the draw tool header from tools/.

as known from the blend tool.

All tools have a widget now so none of this stuff is needed any longer.

which implents the handle transform tool's interaction.

The GimpLayer implementation of the GimpItem transform functions,
and the GimpDrawable convert_type() function, apply their operation
to both the layer and its mask.  The subclasses of GimpLayer --
GimpGroupLayer and GimpTextLayer -- override some of these
functions, providing their own logic for the layer part, and
duplicating the mask part.

Avoid this duplication by adding a set of virtual transform and
type-conversion functions to GimpLayer.  Have the GimpLayer
implementaion of the corresponding GimpItem and GimpDrawable
functions use these functions to apply the operation to the layer,
while taking care of the mask themselves.  Have GimpLayer's
subclasses override the new virtual functions, instead of the
GimpItem and GimpDrawable ones.

Note that the existing implementation of convert_type() in
GimpTextLayer neglected to convert the mask, hence text layer masks
retained their old format after conversion.  This issue is fixed as
a side effect of this commit.