Fix Python compiled module linkage and path under Windows

[mlxd]

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Context: Under Windows, CMake was not finding the correct version of Python to compile the wheels against. This was due to the incorrectly named -DPYTHON_EXECUTABLE flag, which should have been -DPython_EXECUTABLE. In addition, the compiled module path was incorrect in the resulting Windows wheel, and required either updating the PYTHONPATH environment variable, or a move of the modules to ensure Lightning worked on the OS.

Description of the Change: This PR fixes the Python version found by CMake, and moves the compiled module location in the resulting wheels to prevent the need for a user to update PYTHONPATH or manually move the resulting modules.

Benefits: Fixes Windows wheels for Lightning.

Possible Drawbacks:

Related GitHub Issues: #398

[mlxd]

NOTE: To ensure testability, I will merge the conflicting files and undo once all test and comments are resolved for the release.

This PR is not to be merged in its current form.

[codecov]

Codecov Report

Merging #400 (65db86f) into master (b8213b6) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #400   +/-   ##
=======================================
  Coverage   99.88%   99.88%           
=======================================
  Files          49       49           
  Lines        4463     4463           
=======================================
  Hits         4458     4458           
  Misses          5        5           

Impacted Files	Coverage Δ
pennylane_lightning/_version.py	100.00% <100.00%> (ø)

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[AmintorDusko]

Nice work, @mlxd!
Thank you for the quick fix!

[multiphaseCFD]

Thanks Lee for the nice work!

[chaeyeunpark]

Thanks @mlxd for fixing this. I also installed wheels using Windows+conda, which works well.

[mlxd]

Updating for merge onto master. Release tagged as v0.28.1_release