qt-build-utils can invoke qmake when it is a script

[SanderVocke]

Ensure qmake is called either through cmd (Windows) or sh (Linux/MacOS).

The main change is this invocation. The rest of the code change is:

• There were two places qmake were previously invoked and they didn't share code. To prevent duplicating this shell wrapper, refactored a bit to ensure they both call the same method to query qmake.
• Due to said refactoring, also had to change the error handling a bit because the error generation moved. Added error types.

[SanderVocke]

I only tested this so far on the "happy case" on Windows (that is to say: when using a qmake .bat wrapper). Will test on other platforms too.

[SanderVocke]

I marked as ready for review.
Tested all combinations of QMAKE=qmake6 and QMAKE=(a qmake wrapper).[sh|bat] on Windows, Ubuntu and MacOS GitHub runners and cxx-qt builds fine with these combinations.

Please advise how to solve the rust formatting error in CI: a simple cargo fmt in the project did not succeed:

C:\sdev\cxx-qt> cargo fmt
error: expected item, found `..`
 --> \\?\C:\sdev\cxx-qt\examples\cargo_without_cmake\src\cxxqt_object.rs:1:1
  |
1 | ../../qml_minimal/rust/src/cxxqt_object.rs
  | ^^ expected item
  |
  = note: for a full list of items that can appear in modules, see <https://doc.rust-lang.org/reference/items.html>

Error writing files: failed to resolve mod `cxxqt_object`: cannot parse \\?\C:\sdev\cxx-qt\examples\cargo_without_cmake\src\cxxqt_object.rs

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (4979207) to head (0629fcc).

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #1284   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           75        75           
  Lines        12772     12772           
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  Hits         12772     12772           

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