Add .hb to Handlebars and samples to Harbour

[lildude]

Description

Improves the detection of Handlebars .hb files by adding support for the extension to Handlebars with a heuristic to differentiate between Handlebars and Harbour.

I've also added samples for Harbour as there aren't any - it was added long before we needed samples - and added and interpreter.

Closes #4727

Checklist:

• I am adding a new extension to a language.
  • The new extension is used in hundreds of repositories on GitHub.com
    • Search results for each extension:
      • https://github.com/search?q=NOT+is%3Afork+path%3A*.hb+%2F%5C%7B%5C%7B.%2B%5C%7D%5C%7D%2F&type=code
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • Harbour:
        • https://github.com/harbour/core/blob/1044334a0d5ee76e91a900a316a262a0ec1cf4c6/config/po2lang.hb
        • https://github.com/harbour/core/blob/1044334a0d5ee76e91a900a316a262a0ec1cf4c6/contrib/gtqtc/hbmk2_qtgt.hb
        • https://github.com/harbour/core/blob/1044334a0d5ee76e91a900a316a262a0ec1cf4c6/tests/langchk.hb
      • Handlebars
        • https://github.com/wecodemore/grunt-githooks/blob/8a026d6b9529c7923e734960813d1f54315a8e47/templates/node.js.hb
        • https://github.com/zix99/sshsysmon/blob/b8ad28168ec92fa71ad694f11ee0c4221a845dbe/sshsysmon/templates/html.hb
    • Sample license(s):
      • Handlebars: Both are MIT
      • Harbour: All are GPL2
  • I have included a change to the heuristics to distinguish my language from others using the same extension.