[core.memory docs] Add warnings about uninitialized memory

[ntrel]

Add some LREFs.
Add warnings for malloc, qalloc, realloc, extend (in source order).

[dlang-bot]

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Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#17061"

[ntrel]

Unrelated:

D:\a\1\s\druntime\test\shared\src\loadDR.c : fatal error C1083: Cannot open compiler generated file: 'D:\a\1\s\druntime\test\shared\generated\windows\release\64.obj': Permission denied
make[2]: *** [../common.mak:113: generated/windows/release/64/loadDR.exe] Error 1