reintroduce the runJavaScript method on QWebEnginePage for Qt 6 #422

Job	Run time
ubuntu (20.04)	10m 57s
oldschool (centos, 7, python-debug, debug)	5m 6s
ubuntu (22.04)	7m 8s
macOS (12, 3.9, 5.9.*, release)	3m 7s
oldschool (centos, 7, python-debug, release)	4m 56s
macOS (12, 3.9, 5.9.*, debug)	3m 53s
oldschool (rockylinux, 9, python3-devel, release)	4m 32s
macOS (12, 3.11, 5.12.*, debug)	1m 41s
windows (win64_mingw73, 3.10, 5.12.*, x64)	5m 48s
windows (win64_msvc2017_64, 3.6, x64, 5.11.*)	7m 4s
windows (win64_msvc2019_64, 3.12, x64, 5.15.*, PythonQtCore PythonQtGui PythonQtMultimedia)	3m 49s
windows (win32_mingw53, 3.6, x86, 5.11.*)	8m 33s
	1h 6m 34s

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