gRPC Errors after heavy usage

[fertrig]

On macOS, the user may see gRPC errors after heavy usage of Monarch, e.g. select many stories, make many changes to trigger hot reloads, launch dev tools, select multiple devices, themes, etc.

The errors look like the following:

[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: gRPC Error (code: 14, codeName: UNAVAILABLE, message: Error connecting: SocketException: Connection failed (OS Error: Too many open files, errno = 24), address = 0.0.0.0, port = 61002, details: null, rawResponse: null, trailers: {})

[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: gRPC Error (code: 2, codeName: UNKNOWN, message: HTTP/2 error: Connection error: Connection is being forcefully terminated. (errorCode: 10), details: null, rawResponse: null, trailers: {})

This bug was introduced in Monarch 2.1.6.