When input files reference sourcemaps in their body with a comment, it
is most likely not to be useful or correct.
The files incoming from Isobuild have sourcemaps metadata on in-memory objects.
processFilesForTarget -> processFilesForBundle
Since the minifiers work on the output of compilers and linkers, there
is no a good definition of a "target" there. "Bundle" is a general term
that we use to describe the whole compiled app with all the packages.
Rename 'mode' and 'minify' to 'minifyMode' consistently (including in
minifier plugin API).
Make minifyMode default to 'development' (fixes some other old bundler
tests).
This doesn't make bundler-assets pass but it gets farther along.
