Avoid using KeyedVector in KeyLayoutMap

There's a supported alternative, std::unordered_map, that we should be
using instead.

Bug: 228005926
Test: atest libinput_tests inputflinger_tests
Merged-In: Ia1f41d17d7ee912534edffe1a1e7655866fa54c6
Change-Id: Ia1f41d17d7ee912534edffe1a1e7655866fa54c6
(cherry picked from commit 577962e532f235c67ea037f0fd7754834b1ff662)