Convert Tetheroffload HIDL to AIDL.

This patch converts Tetheroffload HIDL to AIDL and adds an empty
example implementation.
There are some changes in AIDL HAL:
1. Combine IOffloadConfig and IOffloadControl into IOffload
2. Use AIDL builtin errors exception code with message as return

Bug: b/205762647
Test: m android.hardware.tetheroffload-update-api
      m android.hardware.tetheroffload-V1-ndk
      m android.hardware.tetheroffload-service.example
      atest VtsHalTetheroffloadTargetTest
Change-Id: I9859ff3df608c058786b4e2b91cb6cd5f38e653a
diff --git a/compatibility_matrices/compatibility_matrix.current.xml b/compatibility_matrices/compatibility_matrix.current.xml
index 5e1589b..78d0248 100644
--- a/compatibility_matrices/compatibility_matrix.current.xml
+++ b/compatibility_matrices/compatibility_matrix.current.xml
@@ -697,6 +697,14 @@
             <instance>default</instance>
         </interface>
     </hal>
+    <hal format="aidl" optional="true">
+        <name>android.hardware.tetheroffload</name>
+        <version>1</version>
+        <interface>
+            <name>IOffload</name>
+            <instance>default</instance>
+        </interface>
+    </hal>
     <hal format="aidl" optional="false">
         <name>android.hardware.thermal</name>
         <version>1</version>