Add MoonBit

[tonyfettes]

This pull request adds support to MoonBit programming language.

Description

This pull request adds support to MoonBit programming language. Here are some relevant resources:

• Website: https://www.moonbitlang.com
• GitHub Organization: moonbitlang

Checklist:

• [x] I am adding a new language.
  • [ ] The extension of the new language is used in hundreds of repositories on GitHub.com.
    • Search results for each extension (I removed the KEYWORDS search because common keywords are widely used in other programming languages):
      • https://github.com/search?type=code&q=NOT+is%3Afork+path%3A*.mbt
  • [x] I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • https://github.com/moonbit-community/moonbit-native-benchmark1
      • https://github.com/moonbit-community/moonbit-native-benchmark2
    • Sample license(s): Apache-2.0
  • [x] I have included a syntax highlighting grammar: moonbitlang/moonbit-tmLanguage
  • [x] I have added a color
    • Hex value: #b92381
    • Rationale: This is the color that they use to brand the MoonBit programming language. Similar colors are used in the icons for MoonBit, as you might see in their website.
  • [ ] I have updated the heuristics to distinguish my language from others using the same extension. (After some primitive search on GitHub, I don't think the extension .mbt is used by other languages).