Mono/C#: Remove hard-coded debugger wait at initialization

Mono/C#: Fix Variant -> MonoString* when type is Variant:NIL

Up until now debug builds would always wait up to 500 ms during initialization
to give time for debuggers to attach to the game.
We no longer want this as it increases startup time unnecesarily.
The way forward is to setup the debugger agent as client instead of server.
This way it's the game that connect to the debugger, not the other way around.
If server mode is still desired, suspend=y can be used to indefinitely wait
for the debugger to attach. This all can be specified with the environment
variable 'GODOT_MONO_DEBUGGER_AGENT' when launching the game.

`Variant::operator String()` returns "Null" if the type is `Variant:NIL`.
We must consider that and return a null `MonoString*` instead when marshalling.
This was also causing a "Null" error to be displayed when exporting a game
because null string members would be set to "Null" during hot-reload.

Fix selection on 3D viewport with half resolution

Fix build warning in ustring.cpp on Windows/MSVC platform

Fix ScriptTextEditor encapsulation

Fixes Curve Editor margin

Fix error log when selecting child of Containers

Mono: Copy native and btls libs on macOS

Updates toggle scripts switch tooltip (if user changed the shortcut)

Make right align for calls number in Profiler

Updates docs of AABB and Plane

This reverts commit cafb8883.

Fixes #34405.
Reopens #8799, #24064.

Docs: OptionButton

Complete the documentation and make some existing descriptions a bit
clearer.
Co-Authored-By: Hugo Locurcio <hugo.locurcio@hugo.pro>

Fixed issues with using a relative path in the export window.

Make NetSockets quieter.

Improve the `KEY_MASK_CMD` documentation

Fix toggle scripts panel to allow using shortcut in other areas

Use print_verbose instead of ERR_* for network errors.

Fix crash on Android with no manifest permissions.

API allows for null array of permissions. It is now normalized with an
empty array.

Mono/C#: Fix project export and fix FindLast/GetFile regression

d09193b0 introduced a regression in
StringExtensions.FindLast. StringExtensions.GetFile was also affected as it
relies on FindLast. This in turn broke the project exporter as it uses GetFile.
The cause of the regression is that now FindLast is calling LastIndexOf
with 'startIndex: 0'. This should be 'startIndex: str.Length - 1' instead.

Also fixed another regression in the project exporter:
de7c2ad2 moved 'GodotTools/GodotSharpExport.cs'
to 'GodotTools/Export/ExportPlugin.cs' and in doing so accidently reverted
the changes from commit e4395811.