Add YAML StringUtils.quoteIfNeeded() for safe scalar quoting

[Jenson3210]

Summary

• Adds StringUtils.quoteIfNeeded(String) in org.openrewrite.yaml.internal that quotes YAML scalar values only when syntactically necessary
• Quotes when: value is empty, starts with an indicator character, contains : or #, starts with ---/..., has leading/trailing whitespace, or contains control characters
• Uses minimal quoting: single quotes by default, double quotes only when escape sequences are needed (e.g., value contains ' or control chars)
• Does not quote valid typed values like true, null, 123 — those are valid YAML as-is

Motivation

• This utility addresses the root cause of openrewrite/rewrite-spring#999, where AddSpringProperty fails to quote values containing colons. The quoteValue method in rewrite-spring uses a regex that only matches strings made entirely of special characters, missing mixed values like TODO: Follow this link https://example.com/page.

With this utility in rewrite-yaml, rewrite-spring (and other modules) can replace ad-hoc quoting logic with a spec-compliant implementation.

Test plan

• 43 unit tests covering: already-quoted passthrough, plain strings, empty strings, indicator characters, colon-space/space-hash patterns, document markers, whitespace, control characters, double-quote escaping, URLs, and the exact scenario from rewrite-spring#999
• ./gradlew :rewrite-yaml:test --tests "org.openrewrite.yaml.internal.StringUtilsTest"