Rename one DAP function

When I first started implementing DAP, I had some vague plan of having
the implementation functions use the same name as the request.  I
abandoned this idea, but one vestige remained.  This patch renames the
one remaining function to be gdb-ish.



diff --git a/gdb/python/lib/gdb/dap/next.py b/gdb/python/lib/gdb/dap/next.py
index 290b9b8..75f2fa6 100644
--- a/gdb/python/lib/gdb/dap/next.py
+++ b/gdb/python/lib/gdb/dap/next.py
@@ -56,7 +56,7 @@
 @capability("supportsSteppingGranularity")
 @capability("supportsSingleThreadExecutionRequests")
 @request("stepIn")
-def stepIn(*, threadId, singleThread=False, granularity="statement", **args):
+def step_in(*, threadId, singleThread=False, granularity="statement", **args):
     send_gdb(lambda: _handle_thread_step(threadId, singleThread))
     cmd = "step"
     if granularity == "instruction":