PA: Remove __throw_out_of_range in address_pool_manager

AddressPoolManager uses bitset::set, bitset::reset(size_t), and
bitset::test. These methods invoke std::__throw_out_of_range on bound
check failure.

This introduces an unexpected dependency on std::__throw_out_of_range in
address_pool_manager.o, which causes a symbol conflict in
breakpad_unittests, due to duplicate definitions when linking
PartitionAlloc (example:
https://ci.chromium.org/ui/p/chromium/builders/try/mac-official/6700/overview).

This CL switches to using bitset::operator[]. Unlike the named methods,
operator[] uses _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS (assertions),
thereby eliminating the problematic dependency on
std::__throw_out_of_range.

Change-Id: I81cfe0af9e9e40398cc7f2431e80813d46537952
Cq-Include-Trybots: luci.chromium.try:mac-official
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7516078
Reviewed-by: Stephen Nusko <nuskos@chromium.org>
Reviewed-by: Takashi Sakamoto <tasak@google.com>
Auto-Submit: Ayumi Ono <ayumiohno@google.com>
Commit-Queue: Ayumi Ono <ayumiohno@google.com>
Cr-Commit-Position: refs/heads/main@{#1574358}
NOKEYCHECK=True
GitOrigin-RevId: 5fa1fd0b24c310dc6cf7d74f71f88f4b8e65c191