Support completions for import file paths

[anthony-c-martin]

Closes #14199

Microsoft Reviewers: Open in CodeFlow

[github-actions]

Test this change out locally with the following install scripts (Action run 10113393437)

VSCode

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-vsix.sh) --run-id 10113393437

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-vsix.ps1) } -RunId 10113393437"

Azure CLI

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-cli.sh) --run-id 10113393437

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-cli.ps1) } -RunId 10113393437"

[github-actions]

Dotnet Test Results

    71 files   -     37      71 suites   - 37   24m 2s ⏱️ - 7m 26s
10 971 tests  -     17  10 971 ✅  -     17  0 💤 ±0  0 ❌ ±0 
25 822 runs   - 12 898  25 822 ✅  - 12 898  0 💤 ±0  0 ❌ ±0 

Results for commit 3ace11b. ± Comparison against base commit 4074e15.