Change official builds to use platform-specific VSIXs

[gregg-miskelly]

This PR hopefully completes the work to switch to platform-specific VSIXs. This renames the gulp tasks to give better names and changes the official builds to use the new tasks.

[gregg-miskelly]

@JoeRobich have you seen either of these failures before?

The first failure is because OmnisharpProjectDiagnosticStatus.message.ProjectFilePath was null

  1) OmnisharpReferenceProvider: sln with several csproj's
       "before all" hook for "Returns the reference without declaration":
     Uncaught TypeError: Cannot read property 'replace' of null
      at t.call [as _next] (src/observers/BackgroundWorkStatusBarObserver.ts:17:74)
      at t.__tryOrUnsub (node_modules/rxjs/_esm5/internal/Subscriber.js:192:16)
      at t.next (node_modules/rxjs/_esm5/internal/Subscriber.js:130:22)
      at t._next (node_modules/rxjs/_esm5/internal/Subscriber.js:76:26)
      at t.next (node_modules/rxjs/_esm5/internal/Subscriber.js:53:18)
      at t.next (node_modules/rxjs/_esm5/internal/Subject.js:47:25)
      at t.EventStream.post (src/EventStream.ts:16:19)
      at EventEmitter.<anonymous> (src/omnisharp/server.ts:307:30)
      at k._fireEvent (src/omnisharp/server.ts:248:24)
      at k._handleEventPacket (src/omnisharp/server.ts:738:18)
      at k._onLineReceived (src/omnisharp/server.ts:703:22)
      at Interface._onLine (readline.js:337:10)
      at Interface._normalWrite (readline.js:482:12)
      at Socket.ondata (readline.js:194:10)
      at addChunk (internal/streams/readable.js:309:12)
      at readableAddChunk (internal/streams/readable.js:284:9)
      at Socket.Readable.push (internal/streams/readable.js:223:10)
      at Pipe.onStreamRead (internal/stream_base_commons.js:188:23)


  2) OmnisharpReferenceProvider: sln with several csproj's
       "before all" hook for "Returns the reference without declaration":
     Error: done() called multiple times in hook <OmnisharpReferenceProvider: sln with several csproj's "before all" hook for "Returns the reference without declaration"> of file /home/runner/work/omnisharp-vscode/omnisharp-vscode/out/test/integrationTests/referenceProvider.test.js
      at processTicksAndRejections (internal/process/task_queues.js:93:5)

[JoeRobich]

@JoeRobich have you seen either of these failures before?

It does seem that our integration tests are in a season of flakiness. I can make time to take a closer look.

[gregg-miskelly]

It does seem that our integration tests are in a season of flakiness. I can make time to take a closer look.

Thanks! I kicked off a test checkin to make sure it really isn't from the offline change: #4854

[JoeRobich]

@vzarytovskii @nohwnd With this change we will now have multiple platform specific vsixs to publish to the marketplace instead of a single vsix. See https://github.com/OmniSharp/omnisharp-vscode/releases/tag/v1.23.17-beta2