fix edge case where a file shadows a directory

[pmcelhaney]

Say you have a directory structure like this:

- a
  - b.js
- a.js

The path for "a/b" would be handled by a.js instead of a/b.js. To fix, I completely rewrote the code to load and find modules and put it in a new class called ModuleTree.

[changeset-bot]

🦋 Changeset detected

Latest commit: 7884555

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
counterfact	Patch

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[coveralls]

Pull Request Test Coverage Report for Build 6984412802

• 231 of 245 (94.29%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.5%) to 83.129%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/server/module-tree.ts	220	234	94.02%

Totals
Change from base Build 6978270104:	0.5%
Covered Lines:	2473
Relevant Lines:	3040

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💛 - Coveralls