Custom completions do not work when not exported from a module

[kubouch]

Describe the bug

When custom completion command is defined within a module but not exported, it doesn't work.

How to reproduce

> module spam {
    def compl [] { [ a b c ] }
    export def foo [x: string@compl] { $x }
}

> use spam foo

> foo <tab>  # nothing happens

Expected behavior

The completion should work in this case.

Not sure how custom completions are implemented but rather than looking up the compl name, it should be referenced by DefId.

Screenshots

No response

Configuration

key	value
version	0.59.1
branch	main
short_commit	4f43d75
commit_hash	4f43d75
commit_date	2022-03-07 01:01:29 +00:00
build_os	linux-x86_64
rust_version	rustc 1.59.0 (9d1b2106e 2022-02-23)
rust_channel	stable-x86_64-unknown-linux-gnu
cargo_version	cargo 1.59.0 (49d8809dc 2022-02-10)
pkg_version	0.59.1
build_time	2022-03-07 12:33:32 +02:00
build_rust_channel	release
features	dataframe, default, trash, which, zip
installed_plugins

Additional context

No response

[sophiajt]

@kubouch - can you check if #4801 fixes this issue?