Insert basic/source/runtime/step[012].cxx into
basic/source/runtime/runtime.cxx.

Follow-up to https://gerrit.libreoffice.org/#/c/3373/ .

In many cases the sources for some class have been split up into several
source files, typically suffixed with a number 0, 1, 2 etc. Presumably this
has been done because some compiler years ago was not capable of compiling all
the source for that class at one time, or some other no longer relevant
reason.

It would be nice to get rid of this convention, so that clever compilers have
a better chance of noticing unused private fields in a class, for
instance. Just combining the source files in question into one source file and
removing the old source files from git leads to a discontinuity in version
control history. But the consensus seems to be that this is not such a big
deal.

I picked these sources just because they happened to be the first ones I came
across when looking for files called *0.cxx.

Change-Id: Ia7e8ece9a4374721bbcce6b0e2aba5721436faae