VHDL: all keywords are insensitive

Summary:
BUG: 413409

In the VHDL highlighter all the rules have the insensitive flag, except two, probably by mistake.
I also add ##Alerts in comments.

Reviewers: Framework: Syntax Highlighting, dhaumann, cullmann

Reviewed By: Framework: Syntax Highlighting, cullmann

Subscribers: kwrite-devel, kde-frameworks-devel

Tags: Kate, Frameworks

Differential Revision: https://phabricator.kde.org/D25102