Move clangd-related code from `org.eclipse.cdt.lsp.editor.ui` to `org.eclipse.cdt.lsp.clangd`

[ruspl-afed]

Now we have bundle org.eclipse.cdt.lsp.clangd for clangd-related code

Let's move classes from org.eclipse.cdt.lsp.editor.ui there

Issues for moving tests and removing org.eclipse.cdt.lsp.editor.ui will follow.

[ghentschke]

I am not sure how to handle the clangd specific extension of the serverInterface used in the org.eclipse.lsp4e.languageServer extension which is currently implemented in the org.eclipse.cdt.lsp bundle.
I don't like to move this extension to org.eclipse.cdt.lsp.clangd, since it could lead to circular depenencies between org.eclipse.cdt.lsp and org.eclipse.cdt.lsp.clangd.

Maybe the bundle wich provides the ICLanguageServerProvider could also deliver the class for the serverInterface.

[ruspl-afed]

Maybe the bundle wich provides the ICLanguageServerProvider could also deliver the class for the serverInterface.

This looks like our default choice until we can define several extensions for server interface for LSP4E, I plan to investigate this after bundles reshaping.