Update doxygen

[matetokodi]

This patch depends on https://github.com/jerryscript-project/jerryscript/pull/5096

In this patch:

• Update Doxyfile to version 1.9.1
• Re-enable doxygen CI checker
• Fix some regular comments that should have been doc comments
• Document void return types for functions explicitly
• Move start of some doxygen groups so they are included always, and not left out of certain ifdefs
• Sync mismatched doc comments between some headers and c files
• Ignore some doxygen warnings:
  • Member (function) is not documented in headers
  • Documented empty return type in headers