Qt: Add QMacStylePlugin under macOS

[Zvicii]

Specify library name and version: qt/5.x

Add QMacStylePlugin under macOS by default.

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• I've read the guidelines for contributing.
• I've followed the PEP8 style guides for Python code in the recipes.
• I've used the latest Conan client version.
• I've tried at least one configuration locally with the conan-center hook activated.

[ghost]

I detected other pull requests that are modifying qt/5.x.x recipe:

• del qtmacextras option for non Macos and delete qtwinextras for non … #11449
• qt5: add md4c dependency #11432

This message is automatically generated by https://github.com/ericLemanissier/conan-center-conflicting-prs so don't hesitate to report issues/improvements there.

[ericLemanissier]

This PR probably wants a CI restart

[Zvicii]

it keeps failing due to unexpected error, should I continue to restart CI？

[conan-center-bot]

All green in build 9 (d519bcc029d9b71b66fd85f81a8aee1f02c80cf0):

• qt/5.15.2@:
  All packages built successfully! (All logs)

  Result of export using Conan v2 (informative)

  _{We have started the migration process to Conan v2 and exporting recipes successfully will be required in the future.
  This is just an informative note to gain awareness about the process, no need to take any action. The plan is to enforce smaller steps that are easier to fix and, eventually, this export step will work.}

  ERROR: Error loading conanfile at '/home/conan/w/prod_cci_PR-11321/recipes/qt/5.x.x/conanfile.py': Unable to load conanfile in /home/conan/w/prod_cci_PR-11321/recipes/qt/5.x.x/conanfile.py
    File "<frozen importlib._bootstrap_external>", line 728, in exec_module
    File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
    File "/home/conan/w/prod_cci_PR-11321/recipes/qt/5.x.x/conanfile.py", line 2, in <module>
      from conans import ConanFile, tools, RunEnvironment
  ImportError: cannot import name 'ConanFile' from 'conans' (/opt/pyenv/versions/3.7.13/lib/python3.7/site-packages/conans/__init__.py)
  

• qt/5.15.3@:
  All packages built successfully! (All logs)

  Result of export using Conan v2 (informative)

  _{We have started the migration process to Conan v2 and exporting recipes successfully will be required in the future.
  This is just an informative note to gain awareness about the process, no need to take any action. The plan is to enforce smaller steps that are easier to fix and, eventually, this export step will work.}

  ERROR: Error loading conanfile at '/home/conan/w/prod_cci_PR-11321/recipes/qt/5.x.x/conanfile.py': Unable to load conanfile in /home/conan/w/prod_cci_PR-11321/recipes/qt/5.x.x/conanfile.py
    File "<frozen importlib._bootstrap_external>", line 728, in exec_module
    File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
    File "/home/conan/w/prod_cci_PR-11321/recipes/qt/5.x.x/conanfile.py", line 2, in <module>
      from conans import ConanFile, tools, RunEnvironment
  ImportError: cannot import name 'ConanFile' from 'conans' (/opt/pyenv/versions/3.7.13/lib/python3.7/site-packages/conans/__init__.py)
  

• qt/5.15.5@:
  All packages built successfully! (All logs)

  Result of export using Conan v2 (informative)

  _{We have started the migration process to Conan v2 and exporting recipes successfully will be required in the future.
  This is just an informative note to gain awareness about the process, no need to take any action. The plan is to enforce smaller steps that are easier to fix and, eventually, this export step will work.}

  ERROR: Error loading conanfile at '/home/conan/w/prod_cci_PR-11321/recipes/qt/5.x.x/conanfile.py': Unable to load conanfile in /home/conan/w/prod_cci_PR-11321/recipes/qt/5.x.x/conanfile.py
    File "<frozen importlib._bootstrap_external>", line 728, in exec_module
    File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
    File "/home/conan/w/prod_cci_PR-11321/recipes/qt/5.x.x/conanfile.py", line 2, in <module>
      from conans import ConanFile, tools, RunEnvironment
  ImportError: cannot import name 'ConanFile' from 'conans' (/opt/pyenv/versions/3.7.13/lib/python3.7/site-packages/conans/__init__.py)
  

• qt/5.15.4@:
  All packages built successfully! (All logs)

  Result of export using Conan v2 (informative)

  _{We have started the migration process to Conan v2 and exporting recipes successfully will be required in the future.
  This is just an informative note to gain awareness about the process, no need to take any action. The plan is to enforce smaller steps that are easier to fix and, eventually, this export step will work.}

  ERROR: Error loading conanfile at '/home/conan/w/prod_cci_PR-11321/recipes/qt/5.x.x/conanfile.py': Unable to load conanfile in /home/conan/w/prod_cci_PR-11321/recipes/qt/5.x.x/conanfile.py
    File "<frozen importlib._bootstrap_external>", line 728, in exec_module
    File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
    File "/home/conan/w/prod_cci_PR-11321/recipes/qt/5.x.x/conanfile.py", line 2, in <module>
      from conans import ConanFile, tools, RunEnvironment
  ImportError: cannot import name 'ConanFile' from 'conans' (/opt/pyenv/versions/3.7.13/lib/python3.7/site-packages/conans/__init__.py)