MAYA-105710: fix USD files fail to load on mapped mounted volume.

[HamedSabri-adsk]

This PR fixes the issue with loading usd from mapped drivers.

Steps to reproduce the error:

    Plugin and external drive or USB Drive to your computer.
    Go to Disk Manager.
    Right Click on your connected drive.
    Select "Change Drive Letter and Path..."
    Select "Add".
    Use "Mount in the following empty NTFS folder:"
    Locate the folder you want to mount to.
    Extract the attached folder to that location.
    Open Maya and then open the *.ma file that contains usd with relative path
    Notice that the USD file doesn't load.

Note: Opening the same file if saved on a local drive or a network drive works without issues.

Description:

There is a bug in gulark's filesystem::canonical which fails to properly resolve relative path. C++17 std::filesystem::canonical doesn't have this issue and properly resolves the relative path.

ghc::filesystem::canonical

auto fullPath = ghc::filesystem::path(currentFileDir).append(relativeFilePath); 
// C:\\MOUNT_ME\\RTS\\RTS\\master_files\\..\\referenced_files\\USD\\barrelTests\\Library\\Assets\\Barrels\\Barrels.usd
auto path = ghc::filesystem::canonical(fullPath, errorCode); // error 

std::filesystem::canonical

auto fullPath = std::filesystem::path(currentFileDir).append(relativeFilePath);
//"C:\\MOUNT_ME\\RTS\\RTS\\master_files\\../referenced_files/USD/barrelTests/Library/Assets/Barrels/Barrels.usd"
auto path = std::filesystem::canonical(fullPath, errorCode); // Ok, good 

Workaround:

To work around this, I removed the need to call filesystem::canonical all together since the given path to ArGetResolver().ConfigureResolverForAsset is resolved properly.

maya-usd/lib/mayaUsd/nodes/proxyShapeBase.cpp

Line 660 in 092f520

PXR_NS::ArGetResolver().ConfigureResolverForAsset(fileString);

e.g
C:\\MOUNT_ME\\RTS\\RTS\\master_files\\..\\referenced_files\\USD\\barrelTests\\Library\\Assets\\Barrels\\Barrels.usd

[kxl-adsk]

Great find @HamedSabri-adsk !

We are changing what resolveRelativePathWithinMayaContext is returning, i.e. used to be the canonical version of the path. This path is consumed then by a few different methods inside of proxy shape compute, including opening/finding a layer for a given path. I was wondering how it will work for layer identifiers and whether or not they will include non-canonical paths...but everything seems to be correct there.

I'm fine with the change, but two things would be good considering doing:

1. Creating a defect in gulrak
2. Check with @fabal if this change will work for AL as well. I remember we refactored this method out of the AL plugin so there may be additional dependencies we don't know about that require returned path to be canonical.

[HamedSabri-adsk]

@kxl-adsk Great points. I will log a defect against gulark sometimes today or tomorrow.

@fabal I would be happy to hear your thoughts on this change ? Thanks

[HamedSabri-adsk]

Switching to v 1.5.6 which fixed the bug in ghc::filesystem::canonical

gulrak/filesystem#124

[HamedSabri-adsk]

revert my workaround now that bug is fixed.