Ensure first class inside className in React is migrated

[govizlora]

Summary

1. Handling React className migration

The PR fixes an issue when migrating React components to tailwind v4 with the migration tool, that the first class after className=" is ignored.

For example, when migrating

<div className="shadow"></div>

shadow will not be migrated to shadow-sm .

This is because in is-safe-migration.ts, it tests the line before candidate with regex /(?<!:?class)=['"]$/. This basically skips the migration for anything like foo="shadow", with only exception for Vue (eg. class="shadow").

The PR changes the regex from

/(?<!:?class)=['"]$/

to

/(?<!:?class|className)=['"]$/

which essentially adds a new exception specifically for React's className="shadow" case.

2. Removing redundant rules

Besides, I found that several other rules in CONDITIONAL_TEMPLATE_SYNTAX being redundant since they are already covered by the rule above, so I removed them. If we prefer the previous explicit approach, I can revert it.

Test plan

Tests added for both the Vue and React classes to prevent false negative cases.

[thecrypticace]

Thanks!