[Android] Stop doing manual argument separation in javac.py.

Stop doing nonsensical things like calling str.split() to manually split
option arguments since it obviously breaks arguments with spaces.

Instead, make "--src-dirs", "--javac-includes" and "--classpath"
accumulate its arguments, and just pass them multiple times in
make_apk.py.

BUG=XWALK-1905
Merge pull request #2073 from rakuco/fix-javac-call

[Android] Stop doing manual argument separation in javac.py.