Throw earlier error for duplicate argument names.

Right now, these errors don't happen until the output language is
compiled.

...
[ RUN      ] AidlTest.RejectsDuplicatedArgumentNames
ERROR: a/IFoo.aidl:1.33-35: method 'f' has duplicate argument name 'a'
ERROR: a/IFoo.aidl:1.33-35: method 'f' has duplicate argument name 'a'
[       OK ] AidlTest.RejectsDuplicatedArgumentNames (0 ms)
...

Change-Id: Ia49f3c0bd514ac76cccba2a72a820bcb831dd4b2
Fixes: 117241915
Test: runtests.sh
2 files changed