core: make backtrace_snprint usable with tt_static_buf()

Currently `backtrace_snprint ` indirectly uses `tt_static_buf()` by
itself. As a result its callers cannot use `tt_static_buf()`. With
large enough backtrace stack size buffer passed to `backtrace_snprint`
will be overwritten inside `backtrace_frame_resolve` call.

Part of #5665

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