Avoid allocating memory in platform::outOfMemory()

When OOM happens, [this function](
https://github.com/apple/foundationdb/blob/8d655d7e40db9b0e7f93d4b3c46ef86364a537a4/flow/Platform.cpp#L2420) is invoked to write to `stderr` and to write a trace event. However, the trace event itself will also try allocate memory, which again failed. This loops until the stack is overflow, and the stack trace contains repeated frames from `outOfMemory` to `TraceEvent`.

We should fix `platform::outOfMemory()` to avoid allocating memory inside it.

Start by reading flow/Platform.cpp at platform::outOfMemory() and the TraceEvent path it invokes; confirm where allocations occur during OOM. Done means the OOM path can write to stderr and record its trace event without allocating or recursively re-entering after allocation failure.

Written by the indexing model from the issue text.