Provide functionality to detect "improper qualified access"

[ericphanson]

closes #48

I think I've got the rough functionality working:

julia> ExplicitImports.improper_qualified_names_nonrecursive(ExplicitImports)
1 issues with qualified names were found:
- `parent` has parentmodule AbstractTrees but it was accessed from ExplicitImports at /Users/eph/ExplicitImports/src/qualified_names.jl:78:21

It isn't clear to me whether or not what matters is parentmodule, which, or maybe in 1.11, ispublic... I might mark this experimental and choose to change the criteria later.

before merging, needs:

• [x] tests
• [x] docstring

and possibly in a followup:

• [x] recursive variant
• [x] check_ variant

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 44 lines in your changes are missing coverage. Please review.

Project coverage is 90.60%. Comparing base (d46bc8e) to head (ddef68e).

Files	Patch %	Lines
src/qualified_names.jl	0.00%	44 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #50 +/- ## ========================================== - Coverage 96.47% 90.60% -5.87% ========================================== Files 5 6 +1 Lines 680 724 +44 ========================================== Hits 656 656 - Misses 24 68 +44 ```

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