This commit adds a Find Module implementing the necessary logic to link
against GStreamer, while implementing some extra bits to enhance the
compatibility.
The first addition is the `mobile` target, which implements the
monolithic `gstreamer_android` library, and which here gains
compatibility with Apple's operating systems.
The second addition is the handling of the basic GStreamer libraries as
`--whole-archive` when statically linked, which was ported from the
ndk-build project in Cerbero. This is not easy to do, as CMake suffers
from several issues that impede its proper usage of pkg-config:
- It cannot differentiate between system/compiler specific libraries
e.g. `-lm`, `-ldl`, but especially `-framework Cocoa`.
- It does not support `--whole-archive` natively until 3.27
- It attempts to reorder flags blindly by separating them with spaces,
thus requiring the use of `-Wl,` wrapping or (in the case of Apple
frameworks) manual framework lookup
The third addition is the port of the Fontconfig and ca-certificates
bundling logic.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/6881>
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