[BOLT] Use new assembler directives for EH table emission (#116294)
When emitting C++ exception tables (LSDAs), BOLT used to estimate the
size of the tables beforehand. This implementation was necessary as the
assembler/streamer lacked the emitULEB128IntValue() functionality.
As I plan to introduce [u|s]uleb128-encoded exception tables in BOLT,
now is a perfect time to switch to the new API and eliminate the need
to pre-compute the size of the tables.