retire qt_parse_all_arguments

The internal CMake macro qt_parse_all_arguments is problematic.
For details see the comments in https://codereview.qt-project.org/c/qt/qtbase/+/386547

In short, we cannot use qt_configure_file for CONTENT that contains semicolons.

The arguments of

    qt_configure_file(OUTPUT foo.txt CONTENT "\\foo\\bar\\\\\\\\;narf")

are split into

    arg_OUTPUT: foo.txt
    arg_CONTENT: \foo\bar\\\\
    UNPARSED_ARGUMENTS: narf

because we use qt_parse_all_arguments.

Ideally, qt_parse_all_arguments would use the PARSE_ARGV signature of cmake_parse_arguments. But it cannot, because it's a macro, and said signature is for functions only.

Fix proposal:

• Create a macro _qt_internal_validate_all_args_are_parsed(${result}) and use that at the call sites of qt_parse_all_arguments.
• Replace all usage of qt_parse_all_arguments with cmake_parse_arguments(PARSE_ARGV)
• Remove extra escaping of backslashes from the call sites, if there is any.