[Build] Local build should check for elevation for UI Integration Tests

[michael-hawker]

Describe the bug

The UI Integration tests required to be run in an elevated command prompt, but that doesn't fail until half-way through a build. It's frustrating if you run the build script locally and forget to elevate to have to re-run the build.

We should check for elevation for local builds at the start of the process and either elevate automatically (if possible) or remind the developer to run in elevated mode.

@azchohfi tested that we can use to detect this:

(New-Object Security.Principal.WindowsPrincipal([Security.Principal.WindowsIdentity]::GetCurrent())).IsInRole([Security.Principal.WindowsBuiltInRole]::Administrator)