ICU-20217 Interprets fuzzer data as UCHar* instead of UTF-8. The conversion

ICU-20217 Interprets fuzzer data as UCHar* instead of UTF-8. The conversion
from assumed UTF-8 resulted in an extremely large percentage of Unicode
replacement characters in the data passed to the API under test.

ICU-20217 Uses fuzzer generated bytes to make random selection of locales, converters,
etc., replacing the random number generator. This way the fuzzer can control
the selections.

ICU-20217 Minor follow-ups from code review.
Removes fuzzer target break_iterator_utf32_fuzzer which does not perform
anything useful what the regular break iterator fuzzer target already performs.

ICU-20217 Fixes for-loop body.

ICU-20217 Uses am allocated buffer to pass head-truncated fuzzer data to the
API under test. The fuzzer may otherwise not detect buffer underflow.
by

ICU-20217 Typing fix.

ICU-20217 Fixing typing.

ICU-20217 Improve fuzzer targets, move truncated fuzzer data into a
new buffer to prevent that buffer underflow goes undetected.

ICU-20217 Fixes buffer management of fuzzer-provided data.

ICU-20217 Factor in PR review comments.