Generate path constant for spring-http-interface library

[Natarajan717]

… (fixes #24048)

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  @wing328 could you take a look when you have a chance? You merged my previous two contributions (fix: [JAVA][rest-assured] missing swagger2 tags package import in generated API class #23946, fix: x-pattern-message ignored for list items in Spring generator #23910).

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Summary by cubic

Generates a path constant for each operation in the spring-http-interface library and reuses it in the @HttpExchange annotation, so callers can reference paths without hardcoding strings (fixes #24048).

• Adds a PATH_<OPERATION_ID> constant per operation.
• Updates @HttpExchange's value attribute to reference the constant.
• Adds a test verifying the constant generation and annotation reuse.

^{Written for commit 9e9dd5f. Summary will update on new commits.}

[cubic-dev-ai]

All reported issues were addressed across 2 files

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