Group mterp files

Group hundreds of tiny files into larger files
(but still less than 1000 lines of code each).
This should make editing and reviews simpler.

This CL is just simple file concatenation.
The filenames don't have any meaning any more.

The generated assembly output is still the same.

Test: test-art-host-gtest
Change-Id: Iee493f334999c2e06a72e19d3c065d19c67323f1