Fix GDScriptDocGen not handling named enums properly

[skorpnok]

What problem(s) does this PR solve?

• Closes Named enum key tooltip does not show the value #122585 GDScript: Named enum_members can shadow other constants in the tooltip #122737
  Godot does not show enum values in code hover tooltips #122633 Enum key declaration has no tooltip #122584

Additional information

This PR changes/fixes how GDScriptDocGen stores the constants of named enums. EnumDoc now stores its associated constants instead them being added to the parent class constants. This also fixes a bug that allowed named enums to shadow the doc data of constants of the same name in the parent class.

It also adds a second code path in EditorHelpBit::_get_constant_help_data to check if the p_class_name refers to a named enum. This is a bit ugly but likely the easiest solution. Things could probably be reshuffled a bit to reduce the code duplication in the function but at the cost of being harder to follow.

[skorpnok]

While looking through other issues that seemed related I found other PR's that address the missing tooltip but none of the ones I found address the shadowing problem. #115942 looks like a lot nicer of a way of handling the EditorHelpBit part, however. if wanted I can adapt this PR to follow that approach for it.

[skorpnok]

Closed for now. Upon further inspection removing the named enum constants from the parent class constants may not be a safe change as there are other bits that seem to already expect them there. I still think that having identical names that need filtering in the constants vector is a bad pattern but this needs discussion.

[skorpnok]

The first half of the PR might still be relevant if refined given @dalexeev 's review comment in #113309
Might also be related to #87825