Add consistent-template-literal-escape rule

[costajohnt]

Fixes #2835

Adds a new consistent-template-literal-escape rule that enforces escaping the dollar sign (\${) instead of the opening brace ($\{) or both (\$\{) in template literals.

Summary

There are three ways to escape ${ in a template literal:

• \${ — escape the dollar sign (enforced by this rule)
• $\{ — escape the opening brace
• \$\{ — escape both (redundant)

This rule reports and auto-fixes the latter two patterns.

Details

• Listens on TemplateElement AST nodes
• Skips String.raw tagged templates
• Handles edge cases with preceding escaped backslashes
• Auto-fixable via --fix
• Enabled in recommended config
• Snapshot-based tests covering valid/invalid cases including multiple occurrences and escaped backslash contexts

[sindresorhus]

I think there is one important safety issue here: the auto-fix currently rewrites non-String.raw tagged templates too. That can change runtime behavior for tags that read strings.raw, even when cooked output looks the same. I’d suggest reporting them without a fixer.

[costajohnt]

Good catch — you're right that changing the escape style alters strings.raw for tag functions that inspect raw values.

Updated the rule to only auto-fix untagged template literals. For tagged templates (other than String.raw, which is already skipped entirely), the inconsistency is still reported but without a fixer, so developers can decide manually.