Cleanup and polish single-component slngen script

[Arlodotexe]

The single-component solution generation script was moved to the root of the tooling repository, alongside the all-component solution generation script.

The original script was replaced with a wrapped call to the new script location to allow for gradual upstream updates.

A few new features were also brought over from the "all solution" script to improve usability:

• The -Component parameter allows requesting a specific component by name, rather than by path.
• Checks for ensuring that provided or computed paths are valid before proceeding with sln generation.
• Additional logging output was added to determine where the script is when failing silently during debugging. This was kept for the added transparency during normal use.

This updated script is fully backwards compatible with the original and should still work with our existing per-component .bat invocation.

To use the script from its new location:

# From the consuming repo root directory 
PS D:\Windows> ./tooling/GenerateSingleSolution.ps1 -Component Converters
# or
PS D:\Windows> ./tooling/GenerateSingleSolution.ps1 -ComponentPath ./components/Converters

# From a component directory
PS D:\Windows\components\Converters> ./../../tooling/GenerateSingleSolution.ps1

Either of these can be used to generate the single-component solution, including the -winui and -multitargets parameters.

[michael-hawker]

Yeah, hopefully in the future we can better coordinate the two scripts, as I feel like there's at least 80% overlap between the all and single, eh?