Previously, we would insert `<#code#>` placeholders when inserting missing protocol requirements (both via the Fix-It and the refactor command). Translate them to LSP placeholders before inserting them.
rdar://92161144
With this change, tests pass whether we default to server-side or
client-side filtering. Also duplicate a few interesting tests to run
both ways. A future commit will beef up the test coverage for
server-side filtering specifically.
Work in progress: add a basic implementation for keeping track of the
current completion session, and use the sourcekitd
complete.open/update/close requests.
