Use mPidMap instead of mProcessNames to get process with pid info

With newly introduced mPidMap, we do not need to iterate every process
to find the one we need with pid information. Use mPidMap directly to
accelerate the getting process method.

By doing this, the time consumption of getConfiguration get reduced by
12.5%. The time consumption percentage of getConfiguration in
getOrientationChanging is reduced from around 87% to 41%. Also, in
prepareSurfacesLocked, the time consumption of getOrientationChanging
reduced from 37% to 25%.

Test: go/wm-smoke
Test: ddms
Bug: 129389526
Change-Id: I77511ce3385049e8c812e8e3706482a48457df0c