Awk: fix regex in a function and update syntax for gawk

Summary:

• fix match(str, /it's a regex, not an operator and normal text/)
• fix escaped characters
• add Symbol, Separator Symbol and Control Flow style
• add some functions and keywords.

Reviewers: Framework: Syntax Highlighting, dhaumann

Reviewed By: Framework: Syntax Highlighting, dhaumann

Subscribers: kde-frameworks-devel

Tags: Framework: Syntax Highlighting, Frameworks

Differential Revision: https://phabricator.kde.org/D12854