Fixes https://github.com/geany/geany-plugins/issues/462

Don't convert function pointer to non-function pointer.  This is
undefined behavior, and some older GCC don't like it.

Work around incorrect keybinding handling with multiple layouts so
cut/copy/delete keybindings work via menuitem activation if we failed
to trigger the action ourselves.

Closes #1386.

Instead of having a handler on 2 separate objects, use :select and
:deselect on the same one.  Those signals are appropriate, as the
documentation mentions that submenus are popped up on :select.

Mark the associated menu items sensitive when the menu is hidden, so
that GTK's accelerator handling can trigger them.  This works around
incorrect handling in Geany's code of keybindings coming from multiple
layouts for cut/copy/delete actions.

Partial workaround for #998, #1286 and #1368.

Avoid crash when detaching the widget from the accessible object
without destroying that widget.

In such situations, the widget is still valid but we will have
destroyed the orphaned accessible object.  Thus, we must make sure we
disconnected the signal handlers the late accessible had set up on the
widget, as they won't be implicitly disconnected by widget
finalization in this case.

Fixes #1385.

Updated filetypes.javascript keywords

Fix snippets keybindings not blocking handled events

Closes #1360.

Fix signature of the snippets keybindings callback, properly blocking
further propagation of handled events thus avoiding possibly activating
another action (like a builtin Scintilla keybinding).

Fixes #1354.

api: rework GeanyProxyProbeResults compat symbols as defines

This is a follow-up of #485.

Constants with different namespace in the same enum confuse g-ir-scanner.

Fix the current scope shown in the statusbar

Since the Scintilla C++ lexer started to fold on `()` [1], the code
looking up the current scope is confused whenever the function
signature spans multiple lines.  Fix this by skipping fold levels that
correspond to parentheses.

Fixes #1279.

[1] https://sourceforge.net/p/scintilla/feature-requests/1138/
    imported in 24f91981

Fix some various issues with accessibility code in Scintilla.

We cannot compute the length in characters after the text has been
deleted, so we need to compute it in BEFOREDELETE.  However, we need to
emit the signal once the buffer has actually changed, so we need to
cache the value in-between those events.

This doesn't support nested templates or escaped `es, but at least
handles the most obvious cases for now.

Part of #934.

Closes #1339

It actually introduces a few new things worth mentioning.