More robust enum field's pattern logic

[Vigilans]

Description of the Change

The original logic uses three different patterns to match an enum constant field. This PR replaces them with a two-scope uniform pattern.

Alternate Designs

To solve #211, an alternative would be to add another to match (constructor + code overrides), but it introduces too much duplicate code, and it still cannot highlight correctly when '{' is placed at new line.

Benefits

• Can correctly highlight with all possible combinations of constructor & code overrides
• Can correctly highlight when '{' is placed at new line or with a comment in between
• Patterns are more neat and uniform

Possible Drawbacks

• Undetected possible regression issues

Applicable Issues

Fix #211 Fix redhat-developer/vscode-java#974

[Vigilans]

New commit added to resolve the review conversations.