Fix Signature to check context before converting $ to dot

[jjohnstn]

• add a check in Signature.appendClassTypeSignature to see if a $ is preceded or followed by a dot before assuming it is an inner class and not part of a package name
• add new test to SignatureTests
• for Packages with $ in name causes problems with imports #5056

What it does

See referenced issue.

How to test

See referenced issue.

Author checklist

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

[cdietrich]

might this have been causing eclipse-xtext/xtext#3708

[cdietrich]

@jjohnstn this seems to break a typename like

org.eclipse.xtext.common.types.testSetups.$StartsWithDollar

package org.eclipse.xtext.common.types.testSetups;

public class $StartsWithDollar {

	public static class Builder {}
	
}

cc @iloveeclipse