Update contentFor tag grammar to properly extract arguments

[veken1199]

What are you adding in this PR?

It seems that the grammar we had for content_for did not properly extract the contentFor liquid tag argument and convert them into array.

In this PR we have:

1. Updated the grammar for contentFor liquid tag to support arguments that contain .
2. Updated ValidContentForArguments check to support closest. instead of context.
3. Introduced a new DeprecatedContentForArgument check that reports a warning when contentFor tag contains context.

• 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

[albchu]

LGTM!

[charlespwd]

Other than the nitpick, this LGTM :) Feel free to merge after!