Extract flipper server instantiation

Summary:
^

This is a very small refactoring and addition to the Flipper Desktop app.

The instantiation of FlipperServer was extracted to a separate function.

This a very tiny change that allows to switch the implementation we use for FlipperServer in a more convenient way.

In this same change, an unused function is added which will create a separate FlipperServer instance that uses a web-socket underneath which makes it possible to use with flipper-server.

So, if interested, it is enough to call that function instead of the one currently in use and it will make Flipper connect to flipper-server instead.

https://pxl.cl/24j8R

Reviewed By: passy

Differential Revision: D36440574

fbshipit-source-id: 94ea2ab7208b898a82ac5e7fd7edd9cb824b4810

desktop/app/tsconfig.json

@@ -14,6 +14,9 @@
     {
       "path": "../flipper-common"
     },
+    {
+      "path": "../flipper-frontend-core"
+    },
     {
       "path": "../flipper-server-core"
     },