This is a reland of commit 3b10dda6.

Extra changes:
Be explicit about calling GetModuleHandleA
Do not use the general GetModuleHandle, which may use wide strings
Refactored ConcatenatePath and add tests

GetModuleDirectory should return the full path, not relative.
ANGLE wasn't able to locate the vulkan ICD file because it was
searching down an invalid relative path. This can be fixed by
ensuring the module directory is always the full path.
on some platforms.

Original change's description:
> When loading vulkan, we can be running from any directory. We need
> to change to the module directory to ensure the swiftshader ICD is
> loaded properly. For example, in some Chrome releases, libGLESv2.dll
> and libvk_swiftshader.dll are in a subdirectory relative to chrome.exe
>
> Bug: chromium:1198567
> Change-Id: I9e68927e512b239728fb2903d1a04702508a4948
> Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2873452
> Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>
> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
> Reviewed-by: Jamie Madill <jmadill@chromium.org>

Bug: chromium:1198567
Bug: angleproject:5949
Change-Id: I63fbe93f8492b7f23566f8193b1b8fe784a34f71
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2904586Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>