Import completion improvements

[jeskew]

Small follow-up to #12281 to improve error messaging on incomplete import statements

Microsoft Reviewers: Open in CodeFlow

[github-actions]

Test this change out locally with the following install scripts (Action run 6670357113)

VSCode

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-vsix.sh) --run-id 6670357113

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-vsix.ps1) } -RunId 6670357113"

Azure CLI

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-cli.sh) --run-id 6670357113

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-cli.ps1) } -RunId 6670357113"

[github-actions]

Test Results

     132 files  ±0       132 suites  ±0   3h 56m 8s ⏱️ + 13m 11s
10 685 tests +1  10 685 ✔️ +1  0 💤 ±0  0 ❌ ±0 
51 635 runs  +4  51 635 ✔️ +4  0 💤 ±0  0 ❌ ±0 

Results for commit e4e1f0e. ± Comparison against base commit 7011935.