Editor: Fix same-name (sub)groups interfering in Inspector

[dalexeev]

• Closes Export categories from parent classes are not reloading, and cause "duplicate categories". #71616.
• Fixes Adding @export_group("Texture") adds texture_filter and texture_repeat properties #83336.
• Fixes Exported properties: cannot set two groups with same name under different categories #83662.
• Fixes Weird @export_category, @export_group, @export_subgroup behaviours in extended scripts #89620.

Clear (sub)group hashmaps when changing category.

Before

After

[KoBeWi]

This also fixes issues in some built-in nodes, like Polygon2D which has its own texture section. Not sure if it was reported.

[kleonc]

This also fixes issues in some built-in nodes, like Polygon2D which has its own texture section. Not sure if it was reported.

These seem the same: #83336, #83662.

[dalexeev]

These seem the same: #83336, #83662.

Thanks, I tested and this PR does indeed fix these issues.

[akien-mga]

Thanks!

[akien-mga]

Cherry-picked for 4.2.2.