Encourage static typing now that it has a performance impact

**Your Godot version:** 4.0 Beta 2

**Issue description:** Static typing is still listed as completely "optional feature of GDScript" despite it having performant effect in 4.0 and it is said to avoid using static typing entirely in docs to not confuse users.

**URL to the documentation page (if already existing):** https://docs.godotengine.org/en/latest/community/contributing/docs_writing_guidelines.html#dynamic-vs-static-typing