Update "Static typing in GDScript" page

[dalexeev]

• Closes Automatically cast parameter throws "Cannot convert argument 1 from Object to Object" error godot#82572.
• Partially resolves (no GitHub magic) Default Node GDScript Template has Warnings/Errors with new Untyped Declaration Warning godot#82587.
• Removes references to the "new" feature (3.1 was released a long time ago), as well as unnecessary exclamations inherent in the old style of our documentation.
• Adds a warning about pitfalls of the as keyword.
• Adds mentions of new features:
  • Add an optional untyped_declaration warning godot#81355.
  • GDScript: Add INFERRED_DECLARATION warning godot#82139.
  • GDScript: Add return type covariance and parameter type contravariance godot#82477.
  • GDScript: Allow using local constants as types godot#80964

[ryanabx]

Oops, I should have checked the pull requests before making one of my own, haha

[allenwp]

If you prefer static typing, we recommend enabling the Text Editor > Completion > Add Type Hints editor setting. Also consider enabling some warnings that are disabled by default.

I really like this addition! Thanks for this :)

:ref:Clobal classes <doc_gdscript_basics_class_name>.

I think this is supposed to be "Global classes" (under the "What can be a type hint" heading)

[allenwp]

As you were working on this pull request, I was also working on a blog post that was intended to be a supplemental document to the Static typing in GDScript page. Your proposed changes in this PR helped me improve my blog post! Thanks!

In case my blog post helps inform this docs update, here it is.

[mhilbrunner]

Thanks! Merged. 🎉 Also closed the other PR as superseded. You've been on fire with GDScript docs, great work!