Fix SOS single file support

[mikem8361]

There are various single file issues that need to be fixed in SOS/dotnet-dump:

• dotnet-dump doesn't work on Linux system generated single file core dumps (createdump doesn't work for single file yet). The problem is that the ELF reader in clrmd used by dotnet-dump returns the wrong base address for the single file module. See below for more details.
• Windows single-file dumps (generated by createdump or dotnet-dump collect) do not work under windbg/SOS because the dbgeng doesn't find the DotNetRuntimeInfo export.
• Windows dotnet-dump doesn't work for single-file dumps because the clrmd PE reader needs to implement the export symbol lookup.
• Add Windows single-file support to the fallback runtime enumeration in platform/targetimpl.cpp. Need C++ to lookup PE exports.
• !pe doesn't print any stack trace info for live Windows single-file under dbgeng. !clrstack does work/displays stack trace.
• Add tests for single-file SOS support.
• Remove generating full dumps in SOS test runner for single file apps when supported.
• Enable single file dumps on overflow exception when the exception info is properly is captured in the Windows dump

The clrmd PE symbol export work should mitigate the need for the DOTNET_ENABLE_SOS_SINGLEFILE env var which was added because the dbgeng symbol lookup was so slow.

[mikem8361]

Some details on the clrmd ELF reader single file base address issue:

                Start                 End         Page Offset
    0x000055cc59e80000  0x000055cc59e82000  0x0000000000001e42          <-- the base address what the clrmd ELF reader returns
        /mnt/c/Users/mikem/OneDrive - Microsoft/save/wsl2/builds/singlefile/bin/Debug/net6.0/linux-x64/publish/singlefile
    0x000055cc59e90000  0x000055cc5a618000  0x0000000000001e42
        /mnt/c/Users/mikem/OneDrive - Microsoft/save/wsl2/builds/singlefile/bin/Debug/net6.0/linux-x64/publish/singlefile
    0x000055cc5a627000  0x000055cc5a871000  0x00000000000025c9
        /mnt/c/Users/mikem/OneDrive - Microsoft/save/wsl2/builds/singlefile/bin/Debug/net6.0/linux-x64/publish/singlefile
    ...
    0x000055cc5aeeb000  0x000055cc5aeec000  0x0000000000003446
        /mnt/c/Users/mikem/OneDrive - Microsoft/save/wsl2/builds/singlefile/bin/Debug/net6.0/linux-x64/publish/singlefile
    0x000055ccd398c000  0x000055ccd3a11000  0x0000000000000000          <-- the actual base address
        /mnt/c/Users/mikem/OneDrive - Microsoft/save/wsl2/builds/singlefile/bin/Debug/net6.0/linux-x64/publish/singlefile
    0x000055ccd3a11000  0x000055ccd3c23000  0x0000000000000085

Single file dumps under lldb and windbg (cross-DAC) do work because they both use the DSO chain to enumerate the native modules.