Add implicit nullability to optional module params

[jeskew]

Partially addresses #11883

Microsoft Reviewers: Open in CodeFlow

[github-actions]

Test this change out locally with the following install scripts (Action run 6239866134)

VSCode

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-vsix.sh) --run-id 6239866134

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-vsix.ps1) } -RunId 6239866134"

Azure CLI

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-cli.sh) --run-id 6239866134

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-cli.ps1) } -RunId 6239866134"

[github-actions]

Test Results

     132 files  ±0       132 suites  ±0   3h 22m 48s ⏱️ + 7m 15s
10 540 tests +1  10 540 ✔️ +1  0 💤 ±0  0 ❌ ±0 
50 711 runs  +4  50 711 ✔️ +4  0 💤 ±0  0 ❌ ±0 

Results for commit 5bcf726. ± Comparison against base commit 547c9c4.

♻️ This comment has been updated with latest results.

[majastrz]