qt: splitting out submodules (WIP)

[cho-m]

PR to experiment with splitting out Qt submodules. Will take some time as 39 formulae (ignore sub-splits, e.g. QtMultimedia can be broken down to ffmpeg, gstreamer, etc). Could handle across multiple PRs ignoring qt conflicts.

Main qt formula would be kept as a way of installing all modules via dependencies.

Some advantages:

• When bumping Qt, can make use of cache on re-runs when only some part (usually WebEngine) fails
• When revision bumping as dependent (e.g. ICU), can avoid rebuilding entire Qt
• As formula dependency, can pare down to actual components
• On slower connection, brew fetch-ing multiple smaller packages/bottles could be better than single large one
• For non-default prefix, only need to rebuild qt-base which is relatively quick compared to full build.
• Better handling of QtWebEngine Xcode requirement via depends_on xcode: ["15.3", :build] rather than silently disabling it in bottle

Some disadvantages:

• There will be some overhead/overlap across submodules so may see slightly larger total downloaded bytes and one-time build.
• Maintenance is now split across more formulae.
• Possible issues from Homebrew's layout. At least seems to have better support for this than GStreamer where we had to go in opposite direction (merging multiple formulae together).

---

An alternative would be implementing per-formula split/sub-packages in brew. This is more like MacPorts split via Subports while prior idea is how Linux distros handle Qt. Though the biggest blocker is actually adding feature to brew as something considered for years but low priority.

Another option could be splitting out particular modules that are slow to build like WebEngine.

---

Submodules Checklist

• qt3d
• qt5compat
• qtactiveqt
• qtbase
• qtcharts
• qtconnectivity
• qtdatavis3d
• qtdeclarative
• qtdoc
• qtgraphs
• qtgrpc
• qthttpserver
• qtimageformats
• qtlanguageserver
• qtlocation
• qtlottie
• qtmultimedia
• qtnetworkauth
• qtpositioning
• qtquick3d
• qtquick3dphysics
• qtquickeffectmaker
• qtquicktimeline
• qtremoteobjects
• qtscxml
• qtsensors
• qtserialbus
• qtserialport
• qtshadertools
• qtspeech
• qtsvg
• qttools
• qttranslations
• qtvirtualkeyboard
• qtwayland
• qtwebchannel
• qtwebengine
• qtwebsockets
• qtwebview