Plugin run targets keep running programs, tests and package scripts inside
the target. Language servers and debuggers run on the host again:
- Remove the Language server targets settings page, the project-only
`languageServerTargets` setting and the PHP / Node.js "Language server:
run in target" option.
- Remove debugging through plugin targets; Debug on a plugin target is
refused again. PHP Remote Debug and Python remote configurations with a
path mapping debug programs in containers.
- Remove LSP / DAP message path mapping, read-only container documents and
the `ide-core` path-mapping module that only these used.
- Run-target validation (API 1.5, unreleased) no longer has a `debug`
operation, and debug start no longer takes a request id.