Use discriminator constraint to declare tagged union types when loading ARM JSON models

[jeskew]

Resolves #12331

Microsoft Reviewers: Open in CodeFlow

[github-actions]

Test this change out locally with the following install scripts (Action run 6849987668)

VSCode

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-vsix.sh) --run-id 6849987668

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-vsix.ps1) } -RunId 6849987668"

Azure CLI

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-cli.sh) --run-id 6849987668

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-cli.ps1) } -RunId 6849987668"

[github-actions]

Test Results

     132 files  ±0       132 suites  ±0   4h 50m 0s ⏱️ - 3m 43s
10 684 tests +1  10 684 ✔️ +1  0 💤 ±0  0 ❌ ±0 
51 631 runs  +4  51 631 ✔️ +4  0 💤 ±0  0 ❌ ±0 

Results for commit 86a405b. ± Comparison against base commit 25b94b2.