Turbopack: Only load capsize-font-metrics once (#83654)
## What?
Currently each `next/font` import would cause the capsize-font-metrics
json to be loaded which is 4.2Mb so not super fast to load on machines
with a slower filesystem. On one trace provided it showed 100-160ms
spent on loading for each `next/font` import (each individual font
imported).
On my machine it was more like 10ms per font imported. Worth fixing
either way.
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Co-authored-by: Luke Sandberg <lukesandberg@users.noreply.github.com>
