Consolidate trust logic into IsTrustedBuilder

[runesoerensen]

Summary

Note: This draft PR builds on unmerged changes introduced in #2571 - see runesoerensen/pack@runesoerensen/fix-builder-inspect-trusted...runesoerensen:pack:runesoerensen/consolidate-trusted-builder-logic to inspect only the commits introduced since that branch.

Consolidate all trust checking into IsTrustedBuilder so callers don't need to separately check IsKnownTrustedBuilder(), and use name.ParseReference for consistent reference matching across both known and user-configured builders.

• IsTrustedBuilder now checks both known trusted builders and user-configured trusted builders
• Uses name.ParseReference for consistent reference matching across both sources - entries without a tag match any tag in the repository, entries with a tag require an exact match
• Remove now-unnecessary || IsKnownTrustedBuilder() calls from build.go, config_trusted_builder.go, and builder_inspect.go

Output

Before

$ pack builder inspect paketobuildpacks/builder-jammy-base:latest
...
Trusted: No

After

$ pack builder inspect paketobuildpacks/builder-jammy-base:latest
...
Trusted: Yes

Documentation

• Should this change be documented?
  • No

Related

Resolves #2572