api/system: make stat() call consistent across platforms (lite-xl#1864)

* api/system: make stat() call consistent across platforms

* docs/system: symlink parameter is now available on most platforms

* system: set symlink flag only when path is directory

* docs: document type == nil on linux

Require modversion 2

Added GH Actions CI badge on README.md

Bump 2.0-beta1 version

Integrate language_cpp plugins from lite-pugins

Starts maximized only if it was in previous session

Add NSDocumentsFolderUsageDescription in info.plist

Related to issue lite-xl#203.

Add also NSDesktopFolderUsageDescription.

Add macos minimum OS variable in info.plist

Prepare release 1.16.9

More accurate update rects / show window / present sequence

For the option when we use the SDL_Renderer we change:

- the order of calls to SDL_DestroyTexture/Renderer.
  Reported by valgrind on linux as an error to destroy the
  renderer before the texture.
- the SDL_Renderer and texture are created when the surface is
  initialized before the window is shown

It seems that creating the SDL_Renderer and Texture between the
moment the window was shown and the renderer present was introducing
a flashing blank window because of the time taken to create the
renderer/texture resources.