improve avm module completion readability with suffix labels and prefix descriptions

[polatengin]

Fixes #18957

Description

Improve module completion readability by showing suffix-first labels and de-emphasizing prefixes for long paths (including AVM).

Add unit tests for AVM suffix labels, prefix-typed filtering, and updated private module label expectations.

Changes I made;

• Module path completion now uses suffix label with prefix in label details.
• Sorting favors suffix to keep related modules grouped.
• Tests updated/added to validate new completion UX.

Note: Existing completion behavior preserved; only display/ordering adjusted.

recording.2026-02-05.161521.mp4

Checklist

• I have read and adhere to the contribution guide.

Microsoft Reviewers: Open in CodeFlow

[github-actions]

Test this change out locally with the following install scripts (Action run 21734870864)

VSCode

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-vsix.sh) --run-id 21734870864

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-vsix.ps1) } -RunId 21734870864"

Azure CLI

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-cli.sh) --run-id 21734870864

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-cli.ps1) } -RunId 21734870864"