Make `to_pipe_at_cursor/3` public to facilitate testing. I think we
should still keep some integration-level testing, but I think the
majority of the test cases can be simplified. I didn't implement making
`from_pipe_at_cursor/3` public, but I think it would make sense as well.

Introduce `ElixirLS.LanguageServer.Protocol.TextEdit` and return it from
`to_pipe_at_cursor/3` and `from_pipe_at_cursor/3`

Add an example of a working simpler test, and add a few examples of
broken tests (as mentioned in elixir-lsp#521 (review))

…d-changes

Proposed changes

Changed the function call detection to not "jump forward", as part of
this if the user requests an index that is not on a function call, then
no action is performed.

Also fix handling of piping function calls that span multiple lines by
adjusting the returned line and column to point to the correct start
location by counting backward.

Handle more cases for manipulating pipes

Co-Authored-By: Jason Axelson <[email protected]>