Replace leftover gtk-doc syntax (#Type) with backquotes.

Matthias Clasen authored Feb 21, 2021 and Emmanuele Bassi committed Mar 11, 2021

Convert links, make things more concise.

We use a compilation symbol in our build to allow the inclusion of
specific headers while building GTK, to avoid the need to include only
the global header.

Each namespace has its own compilation symbol because we used to have
different libraries, and strict symbol visibility between libraries;
now that we have a single library, and we can use private symbols across
namespaces while building GTK, we should have a single compilation
symbol, and simplify the build rules.

Remove all the old 2.x and 3.x version annotations.
GTK+ 4 is a new start, and from the perspective of a
GTK+ 4 developer all these APIs have been around since
the beginning.

It's where we include all our external dependencies.

This way, we don't have to include it in all headers again and again.

This mirrors GTask.

This completes the local clipboard code.

Don't return a const GValue, that's ugly API. Instead require people to
pass in a preinitialized GValue and set that one.

Add infrastructure to do GInputStream => GType conversions. Use that to
implement gdk_clipboard_read_value() which reads into GValues.