Add a README and a standardizable VERSION

* Changes the compatbility matrix version to 5.0 & marks optional
* Tweaks the interface name in case it doesn't get removed soon
  (otherwise readme looks silly)
* Adds a README.md to mapper/stable-c
* Adds VTS test to validate versions match

Test: build + mapper VTS

Change-Id: I9b1256e07aaf2876d579a5487d2051c60097fb70
diff --git a/compatibility_matrices/compatibility_matrix.current.xml b/compatibility_matrices/compatibility_matrix.current.xml
index 71afee3..c665799 100644
--- a/compatibility_matrices/compatibility_matrix.current.xml
+++ b/compatibility_matrices/compatibility_matrix.current.xml
@@ -359,6 +359,7 @@
             <instance>default</instance>
         </interface>
     </hal>
+    <!-- Either the native or the HIDL mapper HAL must exist on the device -->
     <hal format="hidl" optional="true">
         <name>android.hardware.graphics.mapper</name>
         <!-- New, non-Go devices should use 4.0, tested in vts_treble_vintf_vendor_test -->
@@ -846,9 +847,10 @@
             <instance>default</instance>
         </interface>
     </hal>
-    <hal format="native">
+    <!-- Either the native or the HIDL mapper HAL must exist on the device -->
+    <hal format="native" optional="true">
         <name>mapper</name>
-        <version>1.0</version>
+        <version>5.0</version>
         <interface>
             <name>I</name>
             <regex-instance>.*</regex-instance>