Refactoring class/record duplicates switch guard clause in case statements

[homberghp]

Closes #8495.

Added test, to show the problem is real.

Changed org.netbeans.modules.java.source.save.CasualDiff.java

netbeans/java/java.source.base/src/org/netbeans/modules/java/source/save/CasualDiff.java

Lines 2133 to 2136 in 37f95bd

	if (Objects.equals(oldT.getCaseKind(), newT.getCaseKind())) {
	tokenSequence.moveNext();
	copyTo(localPointer, localPointer = tokenSequence.offset());
	} else {

Line 2135 copies too much because localPointer is not properly advanced.

Solution: move localPointer to behind token that precedes the COLON od ARROW token.
Then copy, preserving the space that (optionally) precedes the COLON or ARROW from the updated localPointer
to the offset of COLON or ARROW.

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[homberghp]

Cleanup as necessary to prepare the PR for review.