We used to detect the `rcc` features before every `rcc` list invocation
wich resulted in `rcc` be called twice for every listing operation.
Now we detect the `rcc` list capabilities once during configuration and
pass it to the cmake_autorcc target in the info file.
Introduces the standalone RCC generator class `cmQtAutoGeneratorRcc`.
Every instance of `cmQtAutoGeneratorRcc` class handles the
`rcc` invocation for a single `.qrc` file.
The class will be used in the future to allow parallel `.qrc` file
processing by calling `cmake -E cmake_autorcc <INFO_FILE> <CONFIG>`.