qt: raise conan libs priority vs system libs

[ericLemanissier]

Specify library name and version: qt/5.15.2

fixes #5824
fixes #5931

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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:

• add qt5::x11extras module #6030
• Bugfix/qt packages not used in requires #5997
• test qt components #5922

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

[AndreyMlashkin]

worked for me locally

[AndreyMlashkin]

@SpaceIm @CAMOBAP @ruilvo @Renari
Please approve somebody

[ruilvo]

@AndreyMlashkin I'm not a conan dev hahaha My approvals do nothing. Also, there's a feature on the right sidebar to ask for reviews :)

edit: and also, notice the bot writes things pending review here, so the devs will notice them :)

[CAMOBAP]

@AndreyMlashkin the same to me, I haven't permissions to approve

[ericLemanissier]

trigger CI

[conan-center-bot]

All green in build 4 (a0c3c3fb3e628d4a925f127dce83749557dc633f):

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