build: add cmake support for qt6

[dabbinavo]

features:

• add option to specify target qt version
• dynamically locate QT version and use version specific components and linker targets (also see https://doc.qt.io/qt-6/cmake-qt5-and-qt6-compatibility.html#supporting-older-qt-5-versions)

fixes:

• revert minimum required cmake version to 3.2 (was incremented accidentally in commit ebb3e5e)
• remove duplicate compile definitions for 1D barcode support
• include qt components multimedia, svg, quick and quickcontrols2 only when neccessary

[dabbinavo]

looks good for me. But i can't check build manually

@EndrII, what do you mean by "can't check build manually"

I successfully build the library for Qt5.15.2 and Qt6.2.2 with the following settings (total of 4 builds):

Build A

cmake_minimum_required(VERSION 3.2)

project(test)

SET(QZXING_MULTIMEDIA ON)
SET(QZXING_USE_DECODER_1D_BARCODES ON)
SET(QZXING_USE_DECODER_QR_CODE ON)
add_subdirectory(ext/qzxing/src)

Build B

cmake_minimum_required(VERSION 3.2)

project(test)

SET(QZXING_USE_ENCODER ON)
add_subdirectory(ext/qzxing/src)

[EndrII]

Where are BOSS of this project ?) @ftylitak please check this PR and merge if all is good.

[dabbinavo]

@ftylitak anything missing?