[LiquidDoc] Parser support for optional parameters

[jamesmengo]

What are you adding in this PR?

Adds parser support for [ and ] delimiters around the stringName, which indicate that a param is optional

Within the code, I'm storing this as 'required' rather than 'optional'. The default will be required: true

@param [paramName]

What's next? Any followup issues?

What did you learn?

Before you deploy

• This PR includes a new checks or changes the configuration of a check
  • I included a minor bump changeset
  • It's in the allChecks array in src/checks/index.ts
  • I ran yarn build and committed the updated configuration files
    • If applicable, I've updated the theme-app-extension.yml config

• I included a minor bump changeset
• My feature is backward compatible

• I included a patch bump changeset

[jamesmengo]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• [LiquidDoc] Hover: Wrap optional parameter names in [] #735
• [LiquidDoc] Formatting support for optional @param delimiters [] #734
• [LiquidDoc] Parser support for optional parameters #733 👈 (View in Graphite)
• [LiquidDoc] Prevent rendering of hover tooltip for snippets with no renderable content #729
• [LiquidDoc] Add snippet hover support inside of {% render %} tag #703 : 2 other dependent PRs (#719 , #726 )
• Add parsing + prettier support for @param in {% doc %} tags #646 : 3 other dependent PRs (#652 , #665 , #691 )
• Add basic {% doc %} tag parsing support #621 : 2 other dependent PRs (#636 , #638 )
• main

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