Add automatic default value for primitive type fields

Primitive type fields are auto-initialized with '\0' when not specified.

(This is a non-trivial cherry-pick of
f04d003b4f5fa9f8ee73b6b560c897de45e644cd)

Bug: 206718630
Bug: 206718630
Test: aidl --lang cpp -o out -h out \
  tests/android/aidl/tests/StructuredParcelable.aidl
Test: aidl --lang ndk -o out -h out \
  tests/android/aidl/tests/StructuredParcelable.aidl
Merged-In: I15cfe2a90c0c9adca1692d9a9c997901b90bbbb6
Change-Id: I15cfe2a90c0c9adca1692d9a9c997901b90bbbb6
3 files changed