Check live options when determine what java level is used for parsing

[laeubi]

Currently the Parser determines what java version is parsed once in the
constructor and store them into (modifiable) fields. This causes issues
when the options are modified as everything else works but this
particular fields are not updated.

Instead of having a way to update those fields and as they do not cache
any complex computations, this fields are now replaced with appropriate
getters like it is already done in some cases.

Fix #4849

[laeubi]

@stephan-herrmann can you review? This now passes the enhanced test-case with check for new language levels.

[Copilot]

Pull request overview

This PR refactors the Parser class to dynamically check Java version options instead of caching them in static fields. This enables proper multi-release JAR support where different source folders need different Java Language Specification (JLS) levels.

Changes:

• Removed static boolean fields (parsingJava*Plus, previewEnabled) from Parser that were set once in the constructor
• Replaced field access with dynamic getter methods that check this.options.sourceLevel on each call
• Added a test case with Java 21 features (pattern matching, text blocks) to verify multi-release compilation

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
Parser.java	Removes cached parser version fields, adds dynamic getter methods that check options live, enabling proper multi-release support
CompletionParser.java	Updates single reference from field to method call for preview feature check
MultiReleaseTests.java	Adds test case with Java 21 features to verify multi-release compilation works correctly

Comments suppressed due to low confidence (1)

org.eclipse.jdt.core.compiler.batch/src/org/eclipse/jdt/internal/compiler/parser/Parser.java:13331

• Inconsistent spacing around null comparison operator. The codebase predominantly uses spaces around != (e.g., != null), but this code uses !=null without spaces. For consistency, consider using spaces: this.options != null.

	return this.options!=null && this.options.sourceLevel >= ClassFileConstants.JDK9;
}
protected boolean isParsingJava10Plus() {
	return this.options!=null && this.options.sourceLevel >= ClassFileConstants.JDK10;
}
protected boolean isParsingJava11Plus() {
	return this.options!=null && this.options.sourceLevel >= ClassFileConstants.JDK11;
}
protected boolean isParsingJava14Plus() {
	return this.options!=null && this.options.sourceLevel >= ClassFileConstants.JDK14;
}
protected boolean isParsingJava15Plus() {
	return this.options!=null && this.options.sourceLevel >= ClassFileConstants.JDK15;
}
protected boolean isParsingJava17Plus() {
	return this.options!=null && this.options.sourceLevel >= ClassFileConstants.JDK17;
}
protected boolean isParsingJava18Plus() {
	return this.options!=null && this.options.sourceLevel >= ClassFileConstants.JDK18;
}
protected boolean isParsingJava21Plus() {
	return this.options!=null && this.options.sourceLevel >= ClassFileConstants.JDK21;
}
protected boolean isParsingJava22Plus() {
	return this.options!=null && this.options.sourceLevel >= ClassFileConstants.JDK22;
}

protected boolean isPreviewEnabled() {
	return this.options!=null && this.options.sourceLevel == ClassFileConstants.getLatestJDKLevel() && this.options.enablePreviewFeatures;

---

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[srikanth-sankaran]

Looks good other than that many null checks are provably redundant.

Didn't check the test, only the code changes

[iloveeclipse]

Moving fields access to methods revealed unused code. I would not add unused methods, we have enough dead code in JDT. Beside this should be OK.

[iloveeclipse]

This method can be removed, all callers too, but in a later PR

[iloveeclipse]

@laeubi : could you please squash three last commits into one, so that PR has two commits - one for tests and one for the fix? Thanks.

[laeubi]

Squashed and rebased now.

[iloveeclipse]

OK all tests green, let's merge for RC1.