gdb/testsuite: improve MI support for inferior specific breakpoints

gdb/testsuite: improve MI support for inferior specific breakpoints

In this commit:

  commit b080fe54fb3414b488b8ef323c6c50def061f918
  Date:   Tue Nov 8 12:32:51 2022 +0000

      gdb: add inferior-specific breakpoints

limited support was added in lib/mi-support.exp to help with testing
of inferior specific breakpoints.

Though the changes that were added were not wrong, while working on a
later patch, I realised that I had added the support in the wrong
place -- I only added support to mi_make_breakpoint_multi, when really
I should have added the support to mi_make_breakpoint_1, which is used
by all of the MI procs that create breakpoints.

This commit moves the support to mi_make_breakpoint_1, and updates all
the procs that use mi_make_breakpoint_1 to accept, and then pass
through, and (optional) inferior argument.  This will make it much
easier to write MI tests for inferior specific breakpoints.

There's no change in what is tested after this commit.