Class SpelExpressionParser

Spring's SpelExpressionParser accepts a SpelParserConfiguration, so the signature stays for API compatibility while every expression parses with the defaults and the argument is not applied. The parameter is underscore-prefixed because that is the spelling TypeScript's noUnusedParameters recognises as deliberate, and it cannot be dropped — deleting the constructor would take the argument out of the public type, so new SpelExpressionParser(config) would stop compiling for callers Spring accepts.