src: use std::string for trace enabled_categories
A std::string manages its own memory, so using one removes the implicit assumption that the argv vector passed to node will never be deallocated. Also, the enabled_categories are used to construct a std::stringstream, so its simpler to use the standard library consistently.
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
commit message follows [commit guidelines][]
Affected core subsystem(s)
src