Add functions for parsing and validating access paths

[koesie10]

This adds functions for parsing and validating access paths (such as Argument[foo].Element.Field[foo.Bar.x]) to prepare for future functionality where we're going to be parsing and validating access paths. These functions are not yet used in this PR.

See the description of the access-paths.ts for the reasons for manually parsing the access path rather than simply splitting by . or using a regex.

Example result of parseAccessPathTokens (from the test):

Input: Argument[foo].Element.Field[foo.Bar.x]

Output:

[
  {
    "range": {
      "start": 0,
      "end": 13
    },
    "text": "Argument[foo]"
  },
  {
    "range": {
      "start": 14,
      "end": 21
    },
    "text": "Element"
  },
  {
    "range": {
      "start": 22,
      "end": 38
    },
    "text": "Field[foo.Bar.x]"
  }
]

Checklist

• CHANGELOG.md has been updated to incorporate all user visible changes made by this pull request.
• Issues have been created for any UI or other user-facing changes made by this pull request.
• [Maintainers only] If this pull request makes user-facing changes that require documentation changes, open a corresponding docs pull request in the github/codeql repo and add the ready-for-doc-review label there.

[shati-patel]

Thanks for adding the tests and the clear descriptions! 👍🏽