Recognize a platform binary in ProcessGDBRemote which determines plugins

Complete support of the binary-addresses key in the qProcessInfo packet
in ProcessGDBRemote, for detecting if one of the binaries needs to be
handled by a Platform plugin, and can be used to set the Process'
DynamicLoader plugin and the Target's Platform plugin.

Implement this method in PlatformDarwinKernel to recognize a kernel
fileset at that address, find the actual kernel address in the
fileset, set DynamicLoaderDarwinKernel and PlatformDarwinKernel
in the Process/Target; register the kernel address with the dynamic
loader so it will be loaded later during attach.

This patch only addresses the live debug scenario with a gdb remote
serial protocol connection. I'll handle corefiles in a subsequent
patch that builds on this.

Differential Revision: https://reviews.llvm.org/D133534
rdar://98754861