make extendable bicep parameter files generally available

[polatengin]

Description

• Remove the extendableParamFiles experimental feature gate and related configuration plumbing.
• Update CLI, core, baseline, and language server tests to treat extendable parameter files as enabled by default.
• Move extendable parameter files documentation out of the experimental docs and into the main docs.
• Keep using none completion available for parameter files while avoiding none in quoted file path completions.

Validation

• dotnet test
  • Passed: 14681
  • Failed: 0

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 26248024287)

VSCode

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-vsix.sh) --run-id 26248024287

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-vsix.ps1) } -RunId 26248024287"

Azure CLI

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-cli.sh) --run-id 26248024287

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-cli.ps1) } -RunId 26248024287"

[anthony-c-martin]

This file isn't needed - it should instead go into the official docs.

[mumian]

Content PR - https://github.com/MicrosoftDocs/azure-docs-pr/pull/316534