Replace PowerShell grammar by a better one

[vors]

Replace PowerShell grammar from using https://github.com/sublimetext/powershell to using https://github.com/PowerShell/EditorSyntax .

Description

In #2047 we switched to using https://github.com/sublimetext/powershell for the grammar.
Since then a new project got created: 1 project to rule all the powershell tmLanguage grammars.
https://github.com/PowerShell/EditorSyntax

Today ST switched to using EditorSyntax, and it doesn't make sense anymore to use ST grammar in linguist: it should go directly to EditorSyntax.

cc @omniomi @tylerl0706

Checklist:

• I am associating a language with a new file extension.

  • The new extension is used in hundreds of repositories on GitHub.com
    • Search results for each extension:
      • https://github.com/search?utf8=%E2%9C%93&type=Code&ref=searchresults&q=extension%3AFOOBAR+KEYWORDS+NOT+nothack
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • [URL to each sample source, if applicable]
    • Sample license(s):
  • I have included a change to the heuristics to distinguish my language from others using the same extension.

• 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?utf8=%E2%9C%93&type=Code&ref=searchresults&q=extension%3AFOOBAR+KEYWORDS+NOT+nothack
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • [URL to each sample source, if applicable]
    • Sample license(s):
  • I have included a syntax highlighting grammar.
  • I have included a change to the heuristics to distinguish my language from others using the same extension.

• I am fixing a misclassified language

  • I have included a new sample for the misclassified language:
    • Sample source(s):
      • [URL to each sample source, if applicable]
    • Sample license(s):
  • I have included a change to the heuristics to distinguish my language from others using the same extension.

• I am changing the source of a syntax highlighting grammar

  • Old: https://github-lightshow.herokuapp.com/?utf8=%E2%9C%93&scope=from-url&grammar_format=auto&grammar_url=https%3A%2F%2Fgithub.com%2FSublimeText%2FPowerShell%2Fblob%2F61eac16114081a2de1731092bad41db499678ab3%2FSupport%2FPowershellSyntax.tmLanguage&grammar_text=&code_source=from-url&code_url=https%3A%2F%2Fgithub.com%2FPowerShell%2FEditorSyntax%2Fblob%2F8ec90660044b1729d9724d83c37fec5d40d16186%2Fspec%2Ftestfiles%2Fsyntax_test_TheBigTestFile.ps1&code=
  • New: https://github-lightshow.herokuapp.com/?utf8=%E2%9C%93&scope=from-url&grammar_format=auto&grammar_url=https%3A%2F%2Fgithub.com%2FPowerShell%2FEditorSyntax%2Fblob%2F8ec90660044b1729d9724d83c37fec5d40d16186%2FPowerShellSyntax.tmLanguage&grammar_text=&code_source=from-url&code_url=https%3A%2F%2Fgithub.com%2FPowerShell%2FEditorSyntax%2Fblob%2F8ec90660044b1729d9724d83c37fec5d40d16186%2Fspec%2Ftestfiles%2Fsyntax_test_TheBigTestFile.ps1&code=

• I am adding new or changing current functionality

  • I have added or updated the tests for the new or changed functionality.