Previously we were allocating a separate heap object for each token, which
creates a lot of small objects for the GC to manage. Since we know that
we're always converting from a flat array of native tokens, we can produce
a flat array of writer tokens first and _then_ take pointers into that
array to achieve our goal of making a slice of pointers.
For the use-case of formatting a sequence of tokens by tweaking the
"SpacesBefore" value, this means we can get all of our memory allocation
done in a single chunk and then just tweak the allocated, contiguous
tokens in-place, which should reduce memory pressure for a task which
will likely be done frequently by a text editor integration doing "format
on save".
c233270a9b