Don't compile external module sources

[StephenWeatherford]

Fixes #12758

Microsoft Reviewers: Open in CodeFlow

[github-actions]

Test this change out locally with the following install scripts (Action run 7252241798)

VSCode

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-vsix.sh) --run-id 7252241798

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-vsix.ps1) } -RunId 7252241798"

Azure CLI

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-cli.sh) --run-id 7252241798

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-cli.ps1) } -RunId 7252241798"

[github-actions]

Test Results

       66 files   -        33         66 suites   - 33   28m 13s ⏱️ - 26m 47s
10 436 tests  -        15  10 436 ✔️  -        15  0 💤 ±0  0 ❌ ±0 
25 367 runs   - 12 682  25 367 ✔️  - 12 682  0 💤 ±0  0 ❌ ±0 

Results for commit 19325f6. ± Comparison against base commit 331512e.

♻️ This comment has been updated with latest results.