Also check types when destructuring lsp objects

Also check types when destructuring lsp objects

The problem in this issue is that the disambiguation between Command
and CodeAction objects can only be performed by checking the types of
the keys involved.  So we added that to the spec and check it at
runtime.

* eglot.el (eglot--lsp-interface-alist): Add types to
Command. Tweak docstring.
(eglot--check-object): Renamed from eglot--call-with-interface.
(eglot--ensure-type): New helper.
(eglot--interface): New helper.
(eglot--check-dspec): Renamed from eglot--check-interface.
(eglot--dbind): Simplify.
(eglot-code-actions): Adjust indentation.

* eglot-tests.el (eglot-dcase-issue-452): New test.

GitHub-reference: fix https://github.com/joaotavora/eglot/issues/452