Fix: Syntax highlighting for various issues (#2810)

* highlighter: Fix region & pattern detection

* syntax/sh: Highlight upper case options too

* syntax/c(pp): Try to synchronize the rules to lower the maintenance effort

* syntax/ruby: Fix explicit filename detection in directories

* highlighter: Respect skip rules in regions

* syntax/sh: Fix parameter expansion, cond. flags and generalize filename via ""

* syntax/php|vi: Correct strings in comments to comments only

Additionally improve vimscript comment handling.

* highlighter: Remove problematic start|end check in find(all)Index()

...and additionally remove recursive region end detection

runtime/syntax/justfile.yaml

@@ -2,7 +2,7 @@
 filetype: 'justfile'
 
 detect:
-    filename: '(^\\.?[Jj]ustfile|\\.just)$'
+    filename: "(^\\.?[Jj]ustfile|\\.just)$"
     header: "^#!.*/(env +)?[bg]?just --justfile"
 
 rules: