Adds default (mock) Context Hub HAL 1.2 impl

Also refactors common code.

Bug: 166845383
Test: Compile only (VTS test coming up in future CL)
Change-Id: Iae6cf09e2fffb854af61c29e6004ceb062a892b3
diff --git a/contexthub/1.2/default/OWNERS b/contexthub/1.2/default/OWNERS
new file mode 100644
index 0000000..90c2330
--- /dev/null
+++ b/contexthub/1.2/default/OWNERS
@@ -0,0 +1,3 @@
+arthuri@google.com
+bduddie@google.com
+stange@google.com