[Track2] Add downlevel types to all track2 packages

[chradek]

This issue is to track adding downleveled types to our track2 packages to ensure we support older versions of TypeScript, targeting 3.1 where possible.

What is downleveling?

Just like we can use the TypeScript compiler to downlevel JavaScript code for older runtimes, we can also generate 'down-leveled' types that will work with older versions of TypeScript than the SDK packages use.

Changes

1. Add "downlevel-dts": "~0.4.0", as a devDependency.
2. Update api-extractor.json config so that the dtsRollup.publicTrimmedFilePath points to the new location for the current types.
   E.g. "./types/core-auth.d.ts" -> "./types/latest/core-auth.d.ts"
3. Add the following build:types script to the package.json and update the build script to run it as the last step.
   "build:types": "downlevel-dts types/latest types/3.1"
4. Update the package.json types field to point to the new location from step 2.
   E.g. "types": "./types/core-auth.d.ts" -> "types": "./types/latest/core-auth.d.ts"
5. Add a typesVersions field to the package.json file. This is used to map type declarations based on the version of TypeScript the user is using. Example from core-auth:

"typesVersions": {
    "<3.6": {
      "types/latest/*": [
        "types/3.1/*"
      ]
    }
  },

6. Update the package.json files entry to include types/latest/ and types/3.1/.

Example

Here's an example of making the above changes to the event-hubs SDK:
#8654

Packages to update

Core packages:

• abort-controller
• core-amqp
• core-arm
• core-asynciterator-polyfill
• core-auth
• core-http
• core-lro
• core-paging
• core-tracing
• identity
• logger

Client packages:

• ai-text-analytics
• app-configuration
• event-hubs
• eventhubs-checkpointstore-blob
• cosmos
• keyvault-certificates
• keyvault-keys
• keyvault-secrets
• search-documents
• service-bus
• storage-blob
• storage-file-datalake
• storage-file-share
• storage-queue

[deyaaeldeen]

Closing in favor of #19843