MDEV-38918 Make large pages an explicit per-caller opt-in

[vaintroub]

Summary

my_large_malloc() attempted large pages whenever --large-pages was enabled, silently rounding the size up and reporting it back via an in/out parameter. ut_malloc_dontdump() never passed that adjusted size on to its own callers (the InnoDB redo log buffer and recv_sys_t::tmp_buf), so freeing later used the original, smaller size, causing the reported "faux memory leak".

Only the buffer pool and the MyISAM/Aria key caches are documented to benefit from large pages. Everything else that ended up calling my_large_malloc() only wanted its "do not dump to core" property and picked up large pages as an undocumented side effect; those buffers are also small and sequentially accessed, so they would have gained little from large pages anyway.

• Add MY_TRY_LARGE_PAGES: my_large_malloc() and my_large_virtual_alloc() now only attempt large pages when a caller passes this flag, instead of always trying whenever the global option is set. Only the buffer pool and the key caches pass it.
• The redo log buffer, tmp_buf, and row0log.cc's crypt buffers no longer request large pages at all, removing the size-rounding bug for them without touching that code.
• Fix a broken mtr suppression regex in main.large_pages that would fail the test on Windows.

Test plan

• main.large_pages passes
• Manual repro: mariadbd.exe --large-pages with an oversized buffer pool, confirmed graceful fallback and shutdown reports no leak