freezer: thaw on dumpsys data collection

Introduce a new java API wrapping libprocessgroup to thaw and freeze again
the freezer. Use such API in ActivityManager upon collection of sensitive
dumpsys fields.

Bug: 151225245
Test: manually verified that the freezer is thawed and then frozen again
for meminfo, dbinfo and gfxinfo. Verified that data collection does not
timeout when this API is called

Change-Id: I487f328cb05ceac2fa2f23ad94ca8d4f82b82a5a