Check for Valid Block Targeting

[navdeep5]

What are you adding in this PR?

Resolves #554 and #555

This PR introduces enhanced validation checks for theme blocks, combining two main functionalities:

1. Soft Validation of Nested Blocks

   • Validates that block types referenced in presets adhere to the following criteria:
     • Must be explicitly declared in the root-level blocks array OR
     • The @theme block type must be declared at the root level (exceptions: private blocks)
       
   • Private blocks (prefixed with _) must always be explicitly declared at the root level.
     

2. File Existence Check

   • After the soft validation, the PR ensures that all block type files exist.
     

We are combining these checks into one as they are both responsible for ensuring we have "valid block targets" and it also decreases the number of I/Os required.

What's next? Any followup issues?

With this being a new check, we will want to update https://github.com/Shopify/shopify-dev so users can understand their errors. Developer Docs changes: https://github.com/Shopify/shopify-dev/pull/50568

What did you learn?

This is my first time contributing to this repo so there was a lot to learn in general. However, something that I think will be useful for following checks is being able to traverse the JSON AST of the liquid schema in a controlled and robust manner.

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

[albchu]

Really great start here. Thanks Nav!

[albchu]

Code changes and tophat lgtm. The presets as hash stuff also works like magic.

May you also get eyes from Mia and CP on this before we merge?