Fix param and exception addition/deletion in method signature refactoring

[hopehadfield]

Fixes redhat-developer/vscode-java#3098

[rgrunber]

This looks very good.

The parameter logic seems to be good, and I like that there's a notification for the case when nothing has changed.

I noticed that if I have one exception, and I attempt to change it, I get the "signature and return type unchanged" error, which doesn't seem right.

I think the problem is at https://github.com/eclipse/eclipse.jdt.ls/pull/2754/files#diff-77600cb6e4bae536fc5ccbff3e7d12974c5773c3f446ad8f8956c09335b62973L116 . exception.typeHandleIdentifier is the identifier of the old exception, so even when you change the exception, it gets interpreted as the old one, hence no change. I think what you need here is to only use exception.typeHandleIdentifier if the name of the new exception matches the old one.