dotnet-dump: Add dump location path to DAC/DBI and assembly module search

The dotnet-dump host should add the coredump location directory to the symbol search path for both searching the DAC/DBI modules and for managed assembly modules for getting the metadata when missing from the dump.

Currently the `setclrpath` command needs to be used to set the DAC/DBI path if they can't be downloaded from the symbol server (private build, no network access, etc.). To find the assemblies for the missing metadata type info in commands like clrstack, etc., `setsymbolserver -directory ` needs to be run.

To avoid all the manual error-prone setup, having dotnet-dump add the dump path can make this easier assuming that the DAC/DBI and assemblies are next to the dump.