Add support for Apple framework builds

[Treata11]

Greetings,

In order to enable iOS-derived compilations, I introduced a new flag, LIBDEFLATE_APPLE_FRAMEWORK.
I introduced the required properties for framework generation as described in CMake docs

And building is successful using the following commands:

cmake -S. -B build_iOS \
-DCMAKE_POSITION_INDEPENDENT_CODE=ON \
-DLIBDEFLATE_BUILD_STATIC_LIB=ON \
-DLIBDEFLATE_APPLE_FRAMEWORK=ON \
-DCMAKE_SYSTEM_NAME=iOS

sudo cmake --build build_iOS --target install --config Release

I successfully built LibTiff using the generated framework artifacts.

[Treata11]

Duplicated PR...