Update target_feature to use the attribute template

[ehuss]

New rules:

• ❗ attributes.codegen.target_feature.syntax
• ❗ attributes.codegen.target_feature.duplicates

Removed rules:

• ❌ attributes.codegen.target_feature.info
• ❌ attributes.codegen.target_feature.remark-cfg --- Moved to note
• ❌ attributes.codegen.target_feature.remark-rt --- Moved to note

[rustbot]

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.