www/qt6-webengine: unbreak build on aarch64 (+)

Backport Skia m103 changes to eliminate build error on arm64/aarch64:

In file included from ../../../../../qtwebengine-everywhere-src-6.4.2/src/3rdparty/chromium/third_party/skia/src/core/SkOpts.cpp:46:
../../../../../qtwebengine-everywhere-src-6.4.2/src/3rdparty/chromium/third_party/skia/src/opts/SkRasterPipeline_opts.h:1007:5: warning: 'memcpy' will always overflow; destination buffer has size 2, but
size argument is 8 [-Wfortify-source]

memcpy(&fp16, &h, sizeof(U16));
^

../../../../../qtwebengine-everywhere-src-6.4.2/src/3rdparty/chromium/third_party/skia/src/opts/SkRasterPipeline_opts.h:1032:19: error: functional-style cast from 'neon::F' (aka 'V<float>') to '__fp16'
is not allowed

__fp16 fp16 = __fp16(f);
              ^~~~~~~~

1 warning and 1 error generated.

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