[libcxx] [test] Add a test parameter for disabling memory intensive tests (#68214)

[libcxx] [test] Add a test parameter for disabling memory intensive tests (#68214)

Specifically, the test std/input.output/string.streams/stringstream/stringstream.members/gcount.pass.cpp
allocates a std::string with INT_MAX-1 elements, and then writes this to
a std::stringstream. On Linux, running this test consumes around 5.0 GB
of memory; on Windows, it ends up using up to 6.8 GB of memory.

This limits whether such tests can run on e.g. GitHub Actions runners,
where the free runners are limited to 8 GB of memory.

This is somewhat similar to, but still notably different, from the
existing test parameter long_tests.

(cherry picked from commit 122064a6303eb9c06e0af231f5a4ce145d9a2e67)