Add support for Apple-Framework builds

[Treata11]

Greetings,

I introduced the required properties in CMakeLists.txt to enable cross-compilation for iOS-derived platforms as explained in the CMake documentation.

Binaries of brotlicommon.framework, brotlidec.framework & brotlienc.framework targets will be generated in the build directory with the following commands:

cmake -S. -B build -DBUILD_FRAMEWORK=TRUE -DCMAKE_SYSTEM_NAME=iOS -DBROTLI_BUNDLED_MODE=ON

cmake --build build --target install --config Release

It's also worth noting that I included the BROTLI_PUBLIC_HDRS files for the targets above to ensure they are included in the built framework bundles.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[Treata11]

Addresses issue #1245

[Treata11]

@eustas, Changes above are sufficient to build for iOS-derived platforms & their simulators.
Separate framework bundles are generated for each target:
(brotlicommon.framework, brotlidec.framework & brotlienc.framework).

[eustas]

Thank you this PR.

Please confirm, that FRAMEWORK_VERSION / MACOSX_FRAMEWORK_BUNDLE_VERSION should be semantic (ABI) version. I.e. as of today it will be 2.0.1, not 1.1.0. If not, use existing BROTLI_VERSION (API version)

[Treata11]

Thanks for the review.

Both of the properties are strings that can represent either the ABI or API versions, or even single-letter versioning.
The choice often depends on project conventions or ecosystem requirements

[eustas]

Let's stick then to API version, because those are human readable...