Fix importing tagged unions from compiled JSON

[jeskew]

Resolves #13726

This PR updates the import closure compiler to take account of ARM's discriminator constraint both for type declaration -> TypeExpression conversion and for reference collecting purposes.

Microsoft Reviewers: Open in CodeFlow

[github-actions]

Test this change out locally with the following install scripts (Action run 8474148352)

VSCode

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-vsix.sh) --run-id 8474148352

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-vsix.ps1) } -RunId 8474148352"

Azure CLI

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-cli.sh) --run-id 8474148352

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-cli.ps1) } -RunId 8474148352"

[github-actions]

Test Results

    65 files   -     34      65 suites   - 34   24m 3s ⏱️ - 13m 44s
10 722 tests  -     19  10 720 ✅  -     19  2 💤 ±0  0 ❌ ±0 
25 340 runs   - 12 663  25 336 ✅  - 12 661  4 💤  - 2  0 ❌ ±0 

Results for commit 855485d. ± Comparison against base commit 6b0e259.

♻️ This comment has been updated with latest results.