Tweak new signature logic that checks context of dollar

[jjohnstn]

• modify Signature.appendClassTypeSignature() logic for the
  last segment to use the old logic as it appears there is other
  code that is not prepared for the dollar being part of the class
  name and expects the dollar being converted to dot

What it does

See commit message.

How to test

See #5064 comments.

Author checklist

• I have thoroughly tested my changes
• The change is following the coding conventions
• I have signed the Eclipse Contributor Agreement (ECA)

[iloveeclipse]

• it appears there is other
  code that is not prepared for the dollar being part of the class
  name and expects the dollar being converted to dot

Could you please give more insights? Which code exactly, in JDT or Xtext?

[iloveeclipse]

Is it possible to add test for this?

[Copilot]

Pull request overview

This PR adjusts Signature.appendClassTypeSignature()’s handling of '$' in resolved class type signatures, aiming to restore the pre-#5064 behavior for the last segment (converting '$' to '.') to maintain compatibility with existing downstream code that expects that conversion.

Changes:

• Updated the C_DOLLAR handling in Signature.appendClassTypeSignature() to keep '$' when it appears to be part of a non-terminal segment, but to apply the old '$'→'.' conversion when it appears to be in the last segment.
• Introduced a lookahead scan to detect whether a '.' appears after '$' in certain contexts.

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[jjohnstn]

• it appears there is other
  code that is not prepared for the dollar being part of the class
  name and expects the dollar being converted to dot

Could you please give more insights? Which code exactly, in JDT or Xtext?

In Javadoc of Signature.toCharArray():

Note: This method assumes that a type signature containing a '$'

• is an inner type signature. While this is correct in most cases, someone could
• define a non-inner type name containing a '$'. Handling this
• correctly in all cases would have required resolving the signature, which
• generally not feasible.

I will add a test to SignatureTests.

[jjohnstn]

@iloveeclipse Just to confirm that the two XTest startswithdollar tests run succesfully with this change.

[cdietrich]

can confirm this would make our test green again / restore the old behaviour

[iloveeclipse]

Thanks Jeff for the fast fix & Christian for verification. Looks good, let's merge.