Converted some cancellation tests

src/core/surface/byte_buffer.c

test/core/end2end/tests/cancel_after_invoke.c

test/core/end2end/tests/cancel_before_invoke.c

test/core/end2end/tests/cancel_in_a_vacuum.c

test/core/end2end/tests/cancel_test_helpers.h

test/core/end2end/tests/generate.py