Improve builds speed

[alexdima]

Before	After
build 445464	build 445473

---

1. delete unused .yml files
2. remove unnecessary emsdk setup
3. use a stable cache key to allow for build caches to hit
   https://dev.azure.com/monacotools/Monaco/_build/results?buildId=445464&view=logs&j=61096ea8-10fd-584b-0f03-7b170d825b33&t=0f0ef666-d134-41bd-bd0c-cf8b2aa3f08f&l=15
4. reuse the same patterns to store/restore node_modules as regular vscode
   https://dev.azure.com/monacotools/Monaco/_build/results?buildId=445470&view=results
5. save 20s by minifying only .json files in the root (avoids simulation output and other test outputs/fixtures)
   https://dev.azure.com/monacotools/Monaco/_build/results?buildId=445470&view=logs&j=61096ea8-10fd-584b-0f03-7b170d825b33&t=0891a748-3441-50a4-3e8b-7656cdf5b56b
6. upload the copilot vsix before running the copilot tests, this unblocks all other stages that were waiting on it
   https://dev.azure.com/monacotools/Monaco/_build/results?buildId=445473&view=results

---

Main problems

A. Our Copilot stage was never seeing cache hits e.g.:

##[warning]The given cache key has changed in its resolved value between restore and save steps;
original key: "copilot_build_cache"|n/5xO/gDLWmZP+QQ2uqyTdcsJMwtqurLbQsBTLZa1Zk=|F63S4oMklbJm5DX9SF/yoCjywaM8LiWaBw46dhFrYVk=|y1ia3F6tmEobxRM+AnIUe9mmgc5Az0MAAgVNj3rdWQY=
modified key: "copilot_build_cache"|n/5xO/gDLWmZP+QQ2uqyTdcsJMwtqurLbQsBTLZa1Zk=|F63S4oMklbJm5DX9SF/yoCjywaM8LiWaBw46dhFrYVk=|mbSzeozwjirWVhtb7Q/HgGFfwesSkvbMXK7iA3uJnb4=

B. Our stages were waiting sometimes for 8-9 minutes for the copilot vsix in the "Download Copilot VSIX" stage.

---

In detail

• I found some unused builds [1]
• We're now consuming built wasm, so emsdk is no longer necessary [2]
• I made the cache key stable [3]
• Once I made the cache key stable, I noticed failures caused by the incomplete store/restore [4]
• I noticed that we minify hundreds of json files that we don't ship [5]
• I noticed that the other stages were still just busy-polling wasting minutes waiting for the copilot vsix, so we now publish the vsix before the tests [6]

[Copilot]

Pull request overview

This PR targets faster Copilot extension CI builds by removing the emsdk setup path, deleting legacy Azure Pipeline YAMLs in the extension, and switching the Copilot build cache to a stable, computed cache key.

Changes:

• Remove emsdk setup usage by deleting extensions/copilot/build/setup-emsdk.sh.
• Delete legacy Copilot extension Azure Pipelines (extensions/copilot/build/release.yml, extensions/copilot/build/pre-release.yml).
• Update Copilot pipeline setup to use a computed cache key (.build/packagelockhash) and extend the shared cache-key computation to include a Copilot-specific cachesalt.

Show a summary per file

File	Description
extensions/copilot/build/setup-emsdk.sh	Deleted emsdk bootstrap script previously used to install/activate emscripten.
extensions/copilot/build/release.yml	Deleted legacy Azure Pipeline definition for stable release.
extensions/copilot/build/pre-release.yml	Deleted legacy Azure Pipeline definition for scheduled pre-release.
build/azure-pipelines/copilot/setup-steps.yml	Switch Copilot build cache key to a computed hash file; remove emsdk setup steps.
build/azure-pipelines/common/computeNodeModulesCacheKey.ts	Include Copilot extension .cachesalt in the computed key inputs.

Copilot's findings

• Files reviewed: 5/5 changed files
• Comments generated: 2