floss: shim/stack: add MsftExtensionManager

This patch adds and starts MsftExtensionManager from the shim
for non-Android platforms.

Bug: 246398494
Tag: #floss
Test: ./build.py --target test
Test: Manual test.

Change-Id: I316e9e967ba38f19428dc0aa9c74fe01eda44a4f