Add combinatorial tests for Qt installer

Add combinatorial testing for installer.

Pict tool: https://github.com/microsoft/pict

For example,

• model different possible combinations in the installer,
• set random seed,
• generate covering array,
• use that array as input to a test that installs different combinations,
• occasionally change the seed and rerun to generate new combinations that provide variation but always maintain combinatorial coverage

Test likely needs to be quite generic for the properties it checks.

For example, check that there are no errors generated for any combination. A more advanced one could also model the output in terms of installed directories etc. but just error checks could be a good start.