Add prebuilt_build_tool to allow genrules to use prebuilt tools

cc_prebuilt_binary doesn't work well for host tools because they'll
often be using their own versions of shared libraries that may not be
compatible with what we build.

So add a module type that allows genrules to use one of these prebuilts
as a tool. Like other prebuilts, we'll use the source module if we have
it, or the prebuilt otherwise.

It supports adding extra dependencies for shared libraries or other data
files that are necessary to run the tool. Any genrules using the tool
will be rerun if any of the dependencies change.

Bug: 128690776
Test: treehugger (builds one-true-awk with bison)
Change-Id: I82c26be1c3c9fe6cab42892ddea339c301c0b316