Fix mono on windows path ext error

Mono/C#: Remove GodotTools dependency on the Mono.Posix assembly

MSBuild on Windows uses the system .NET Framework BCL instead of Mono's. Because
of this, it may not be able to find the Mono.Posix assembly, so it's better
not to depend on it. We needed Mono.Posix to call Syscall.access, so we can
replace this with an internal call that does the same in C++.

Makes more editor strings translatable

Mention that bbcode_text += string is a bad idea

* "Add" button text in Groups Editor
* "Receiver Method" in Connect Signal Dialog
* "Play Mode" in Animation State Machine Editor
* "Mesh Library" button text in Mesh Library editor plugin
* Compose Array node button texts in Visual Script
* Various button texts in TileSet Editor
* Various Run Script errors

Mention how to handle cancel in ConfirmationDialog

Fixes property names serialization in project.godot

Set proper icons for FileDialog in editor theme

Always use 16 bit renderbuffer depth on WebGL

Updated docs for many VisualServer methods

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