Don't report exported variables as unused

[jeskew]

Resolves #12268

Microsoft Reviewers: Open in CodeFlow

[github-actions]

Test this change out locally with the following install scripts (Action run 6648674752)

VSCode

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-vsix.sh) --run-id 6648674752

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-vsix.ps1) } -RunId 6648674752"

Azure CLI

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-cli.sh) --run-id 6648674752

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-cli.ps1) } -RunId 6648674752"

[github-actions]

Test Results

     132 files  ±0       132 suites  ±0   4h 11m 10s ⏱️ + 16m 58s
10 679 tests +1  10 679 ✔️ +1  0 💤 ±0  0 ❌ ±0 
51 603 runs  +4  51 603 ✔️ +4  0 💤 ±0  0 ❌ ±0 

Results for commit 24c6ee8. ± Comparison against base commit 914ac3a.