Add set_input_active API, akin to set_output_active

[xdje42]

Is your feature request related to a problem? Please describe.

More complex clients have a need to control which threads are active and which are not for longer simulations.
The proposal is to add set_input_active akin to the existing set_output_active API routine.

Eg,

diff --git a/dynamorio/trunk/clients/drcachesim/scheduler/scheduler.h b/dynamorio/trunk/clients/drcachesim/scheduler/sch\
eduler.h
--- a/dynamorio/trunk/clients/drcachesim/scheduler/scheduler.h
+++ b/dynamorio/trunk/clients/drcachesim/scheduler/scheduler.h
@@ -1269,6 +1269,7 @@ protected:
         bool needs_init = false;
         bool needs_advance = false;
         bool needs_roi = true;
+        bool active = true;
         bool at_eof = false;
         uintptr_t next_timestamp = 0;
         uint64_t instrs_in_quantum = 0;
@@ -1748,6 +1749,9 @@ protected:
     stream_status_t
     set_output_active(output_ordinal_t output, bool active);

+    scheduler_status_t
+    set_input_active(int workload_ordinal, memref_tid_t, bool active);
+
     // Caller must hold the input's lock.
     void
     mark_input_eof(input_info_t &input);