Implements https://www.edgedb.com/docs/edgeql/index

Description

Adds grammars, language definition, and adds test case.

Checklist:

• 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:
      • https://github.com/search?q=extension%3Aedgeql+NOT+nothack&type=Code
      • https://cs.github.com/?scopeName=All+repos&scope=&q=path%3A*.edgeql

  • I have included a real-world usage sample for all extensions added in this PR:

    • Sample source(s):
      • https://github.com/edgedb/edgedb-examples
    • Sample license(s):
    • https://github.com/edgedb/edgedb/blob/master/LICENSE
  • I have included a syntax highlighting grammar: https://github-lightshow.herokuapp.com/
  • I have updated the heuristics to distinguish my language from others using the same extension.