ts-loader with thread-loader doesn't work in transpileonly mode #1618

Expected Behaviour

When using the thread-loader, the ts-loader checks for hasForkTsCheckerWebpackPlugin to enable transpile only mode,
but since the settings are stringified and parsed again, the constructor name is Object and not ForkTsCheckerWebpackPlugin anymore. There needs to be another way of using transpile only, eg via happypackmode or similar.

Actual Behaviour

The hasForkTsCheckerWebpackPlugin always returns false disabling the transpileonly mode.

Steps to Reproduce the Problem

use thread-loader with forktscheckerwebpackplugin and output the value of hasForkTsCheckerWebpackPlugin

Location of a Minimal Repository that Demonstrates the Issue.