Replace KeyedVector with unordered_map in dispatcher

To modernize the code base and increase readability, use
std::unordered_map instead of KeyedVector inside InputDispatcher. This
helps understand the code flow, and allows some foreach expressions,
thus removing shadow variables.

Bug: 142017994
Test: presubmit
Change-Id: I969fc03dc38e258e9f3d0f2e60c9534515ce2926
Merged-In: I969fc03dc38e258e9f3d0f2e60c9534515ce2926