[Refactor] Use partition helper in filterRegexValues

[github-actions]

WHY are these changes introduced?

filterRegexValues in packages/theme/src/cli/utilities/asset-ignore.ts hand-rolled a split of ignore patterns into negated (!-prefixed) and normal ones. It walked the list three times — filter for the negated patterns, map to strip the !, then a second filter with the inverted predicate — and shadowed the regexList parameter name in each callback, so the predicate read as regexList.startsWith('!') on what is actually a single pattern.

@shopify/cli-kit/common/collection already exports a partition helper for exactly this, and it is already used elsewhere in the repo (packages/app/src/cli/services/deploy/upload.ts).

WHAT is this pull request doing?

Replaces the three-pass split with a single partition call, and renames the callback parameter to pattern so it describes the element rather than the list.

The return type is now an explicit [string[], string[]] tuple. That makes the = [] destructuring defaults at the three call sites provably unreachable, so they are removed — the array-literal return could never have produced undefined elements, and the defaults only obscured that.

Behavior is unchanged: partition keeps the truthy group first, so the negated group is destructured first and then has its ! prefix stripped, preserving the original [normalPatterns, negatedPatterns] return order and relative ordering within each group.

How to manually test your changes?

In a theme directory with a .shopifyignore containing a mix of normal and negated (!-prefixed) patterns:

shopify theme push --dry-run
shopify theme pull --only "templates/*.json"
shopify theme push --ignore "assets/*" --ignore "!assets/keep.css"

Files matching a negated pattern should still be included, exactly as before.

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is user-facing — I've identified the correct bump type (patch for bug fixes · minor for new features · major for breaking changes) and added a changeset with pnpm changeset add