fix(shortcuts): find target in dir and Path

[kengwang]

Description

The shortcut target should find where the target is just like where the shim creation does. Not just append to $dir

Motivation and Context

Closes #6243

How Has This Been Tested?

It now can successfully create the shortcut below

"shortcuts": [
        [
            "java",
            "App",
            "-jar \"$dir/App.jar\""
        ]
    ]

and it won't break the backward compatibility

Checklist:

• I have read the Contributing Guide.
• I have ensured that I am targeting the develop branch.
• I have updated the documentation accordingly.
• I have updated the tests accordingly.
• I have added an entry in the CHANGELOG.