Read protobuf output instead of parsing text.

`dumpsys meminfo` provides an `--proto` option to output a protobuf
instead of text. This is easier to consume than parsing text and is more
resistant to changes in the text format, like when RSS was recently
added.

Fixes: 143890260
Test: atest CollectorsHelperTest:com.android.helpers.tests.DumpsysMeminfoHelperTest
atest CollectorDeviceLibTest:android.device.collectors.DumpsysMeminfoListenerTest

Change-Id: I6f9a63f2b5088e9401627cd2c0d81ae2d384cf51