[Feature Request] Support C# 14 extension blocks API metadata generation

[filzrev]

Is your feature request related to a problem? Please describe.
docfx v2.78.5 add support for C# 14 syntax.

But currently it don't generate API metadata when using Extension Blocks syntax.
It need to add support for Extension Blocks syntax. supports.

Describe the solution you'd like

• Create static class page that using Extension Blocks
• Show extension members on Extension Blocks receiver type API page. (Similar to extension methods)