[identity] Migrate to ESM

[maorleger]

This issue tracks migrating identity to ESM, vitest, and tshy

There are a few blockers for identity that we still need to resolve as part of this, and it'll likely benefit from migrating later on after more packages have migrated.

Issues:

• MSAL: Incorrect type definitions for msal-browser and msal-react AzureAD/microsoft-authentication-library-for-js#6781 typings are incorrect. Either work with MSAL to fix typings or come up with a workaround
• @azure-tools/test-* packages use @azure/identity as a dependency for the test credential. Because of how dev-tool rewrites imports for the package under test we will need to figure out how to exclude this rewrite when testing identity, or scope it to avoid rewriting files in test-credential for identity imports

Rush Multi-Project Build Tool 5.120.6 - Node.js 20.10.0 (LTS)
> "dev-tool run test:vitest --no-test-proxy"

[dev-tool/register] Rewrote import of "@azure/identity" to "../../../../../sdk/identity/identity/src/index".
Trace: [Internal Error] Error [ERR_REQUIRE_ESM]: Must use import to load ES Module: /home/maorleger/workspace/azure-sdk-for-js/sdk/identity/identity/src/index.ts
require() of ES modules is not supported.
require() of /home/maorleger/workspace/azure-sdk-for-js/sdk/identity/identity/src/index.ts from /home/maorleger/workspace/azure-sdk-for-js/common/tools/dev-tool/src/util/browserRelayServer.ts is an ES module file as it is a .ts file whose nearest parent package.json contains "type": "module" which defines all .ts files in that package scope as ES modules.
Instead change the requiring code to use import(), or remove "type": "module" from /home/maorleger/workspace/azure-sdk-for-js/sdk/identity/identity/package.json.

Is the error due to this

• node:http is being mocked in the test setup; however, a better approach is to pass a custom httpClient with the correct responses as done in this proof-of-concept