Fix scalar YAML aliases in loadYamlContent

[Copilot]

loadYamlContent() returned BCP340 for valid YAML aliases targeting scalar values, despite supporting mapping aliases.

• YAML parsing

  • Parse through SharpYaml’s document model before converting to an object.
  • Preserve reference handling while allowing resolved scalar aliases to be converted normally.

• Regression coverage

  • Add unit coverage for scalar anchor/alias deserialization.
  • Add compilation and output evaluation coverage for loadYamlContent().

source: &CIDR 10.0.0.0/17
alias: *CIDR

{
  "source": "10.0.0.0/17",
  "alias": "10.0.0.0/17"
}

• Fixes loadYamlContent still fails for scalar YAML aliases in v0.46.1 with BCP340 #20119

[github-actions]

Test this change out locally with the following install scripts (Action run 31044003704)

VSCode

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-vsix.sh) --run-id 31044003704

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-vsix.ps1) } -RunId 31044003704"

Azure CLI

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-cli.sh) --run-id 31044003704

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-cli.ps1) } -RunId 31044003704"