Envrionment provides access to env vars and system properties

When accessing analytics from AGP we need to use Gradle APIs in
order to access system properties and env variables. This CL
expands Envrionment API to support accessing system properties.
Any system property read should use this API.

From the AGP side a Gradle-specific implementation of Environment
is provided and set during initialization.

Bug: 148512507
Test: existing
Change-Id: Ic323c445774a6a4e59d05ddddeae2fdb28d0228b
6 files changed