Add const annotations to dispatcher

These allow us to dump the dispatcher state from other const dispatcher
methods.

Bug: 274073185
Test: m
Change-Id: I483d957b243bca595c147656d8305fdc4f43fb33
diff --git a/services/inputflinger/dispatcher/LatencyAggregator.cpp b/services/inputflinger/dispatcher/LatencyAggregator.cpp
index a5bfc25..96d78c3 100644
--- a/services/inputflinger/dispatcher/LatencyAggregator.cpp
+++ b/services/inputflinger/dispatcher/LatencyAggregator.cpp
@@ -256,7 +256,7 @@
     }
 }
 
-std::string LatencyAggregator::dump(const char* prefix) {
+std::string LatencyAggregator::dump(const char* prefix) const {
     std::string sketchDump = StringPrintf("%s  Sketches:\n", prefix);
     for (size_t i = 0; i < SketchIndex::SIZE; i++) {
         const int64_t numDown = mDownSketches[i]->num_values();