test: improve validation of report output
This commit improves the validation of generated diagnostic reports. This enforces the general report schema. Next steps include tighter validation of various libuv handle types, and checking for specific values (such as an error message or stack frame).
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
commit message follows commit guidelines