This commit refactors our use of translate-c, in preparation for larger
removal of `cImport` and better co-ordination between building of C
dependencies and translation of headers.
The major update is the creation of an internal helper package that
wraps our use of the external translate-c library. This allows us to not
only have better shorthand and a data-driven, declarative approach to C
translation (versus the otherwise more imperative approach), it also
funnels the external dependency into a single package instead of
spreading it out among what will be an increasingly larger amount of
places as dependencies in `pkg/` get updated.
It also includes some refactors, namely to the harfbuzz package, which
has had its individual settings refactored into helpers to allow for the
settings to be better shared between translation and the build of the
c-based static library.
Wuffs has also had a bit of a refactor too so that we don't generate a
file with all of the macro defines in it - we just send these in as `-D`
flags now.
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