Add a fuzzer to fribidi

[ebraminio]

This adds a fuzzer to the project in hope to be added to oss-fuzz later, here is how to use it, first make sure a fairly updated version of clang and lld packages are installed, the second maybe is included in llvm package in your distribution, better to make sure llvm is also installed as llvm-symbolizer is needed for better crash log reports, then run these

CC=clang CC_LD=lld CFLAGS="-fsanitize=address,fuzzer-no-link" meson fuzzbuild --default-library=static -Dfuzzer_ldflags="-fsanitize=address,fuzzer" -Ddocs=false
ninja -Cfuzzbuild
fuzzbuild/bin/fribidi-fuzzer

After a case is found one should put the case in test/fuzzing folder, meson will run those tests using touch meson.build && meson test -C fuzzbuild --print-errorlogs (or one can only trig a case using e.g. fuzzbuild/bin/fribidi-fuzzer test/fuzzing/crash-69ebdb74927bd63911e9af32e7da3b0216279461) making sure there won't be regression with the found cases.

Things can be improved in the fuzzer integration so feedback is welcome as some interesting cases are already found with this (as already added to test/fuzzing) but I can consider those API call issue.

[ebraminio]

Now that the integration is complete you should be able to use oss-fuzz found cases like this, first download the test cases from https://crbug.com/oss-fuzz/34695 and https://crbug.com/oss-fuzz/34696 (you should log in using the email you've put in readme) then for example run:

CC=clang CC_LD=lld CFLAGS="-fsanitize=memory,fuzzer-no-link" meson msanbuild --default-library=static -Dfuzzer_ldflags="-fsanitize=memory,fuzzer" -Ddocs=false
ninja -Cmsanbuild
msanbuild/bin/fribidi-fuzzer clusterfuzz-testcase-minimized-fribidi-fuzzer-5361146803650560

CC=clang CC_LD=lld CFLAGS="-fsanitize=address,fuzzer-no-link" meson asanbuild --default-library=static -Dfuzzer_ldflags="-fsanitize=address,fuzzer" -Ddocs=false
ninja -Casanbuild
asanbuild/bin/fribidi-fuzzer clusterfuzz-testcase-minimized-fribidi-fuzzer-5372192033472512

After fixing the case you can put the fix case in test/fuzzing.

Just reproduced them on a machine, feel free to ask if you got any issue. I will try to see if I can come with a fix. Thanks!