binder_ndk: readData/writeData

These new APIs are similar to Parcel::readData/writeData. They are just
a dispatcher to the actual read/write APIs based on types. This
simplifies the NDK backend code generation.

This is a preparation step to support fixed-size arrays in AIDL.

Bug: 207087196
Test: atest CtsNdkBinderTestCases aidl_integration_test
Change-Id: I2c876a622b0b7d3c379bf05f8416a52cec235854