Adjust qt_add_lrelease and qt6_add_translations after API review

Context
https://git.qt.io/alcroito/qt6-cmake-api-review/-/commit/5313c017d09c51d9034dd62b33f968b9cd54363c#179fb5213a114272e340c63285f9fb35ba530ab8_369_434

In qt_add_lrelease, rename `MANUAL` to `NO_TARGET_DEPENDENCY` or something more clear.

In qt_add_translations:

• If RESOURCE_PREFIX is not specified, by default a create a resource with a prefix set to '/i18n' to match the resource prefix picked up magically by QQmlApplicationEngine.
• Users can change the prefix to one they would like instead of the default.
• If QM_FILES_OUTPUT_VARIABLE is specified, a resource is NOT automatically created anymore, because the files are intended to be installed instead.
• If both QM_FILES_OUTPUT_VARIABLE and RESOURCE_PREFIX are specified, issue FATAL_ERROR.

Mark qt6_add_translations as Technical Preview for 6.2
Reason: We don't feel comfortable committing to this API because we don't know how the project-wide translations use case might affect it.

Add OUTPUT_TARGETS as an out_var for when qt6_add_translations is called on a static library target. This should be populated with the value of OUTPUT_TARETS set by the internal qt6_add_resource call.