GDScript: Fix and improve doc comment parsing

[dalexeev]

• Closes GDScript documentation comments: description tooltips are omitted when applied to @export variables with multiline arguments, as well as @export_category #78934.
• Closes Generated documentation for single line enum duplicates the same documentation for each enumeration #81578.

1. Handle annotations correctly.

2. Handle inline doc comments on multiline declarations. Now this works:

func my_func(): ## Doc.
    pass

class MyClass: ## Doc.
    pass

3. Handle the case of multiple declarations on the same line.

4. Add @tag support for inline doc comments.

Test script

## desc 1
var a1; var a2; var a3 ## desc 2

var b1; var b2; var b3 ## desc 3

## desc 4
var c1; var c2; var c3

enum E1 { A, B, C } ## desc 5

## desc 6
enum E2 { A, B, C }

enum E3 { ## desc 7
    A, B, C
}

enum E4 {
    ## desc 8
    A, B, C
}

enum E5 {
    A, B, C ## desc 9
}

enum E6 {
    A,
    B, ## desc 10
    C,
}

enum E7 { ## desc 11
    A, ## desc 12
    B, ## desc 13
    C, ## desc 14
}

[adamscott]

Approved by the GDScript team. It even reduces the number of lines! That's awesome, thanks @dalexeev

[akien-mga]

Thanks!