Symbols and relationships in a symbol graph are non-deterministically ordered

[QuietMisdreavus]

Radar: rdar://95598551

When emitting a symbol graph, the symbols and relationships can change ordering between runs, even if there are no changes to symbol and relationships data. I believe the ordering is currently determined by the order in which symbols are crawled within the module, but regardless, this causes issues with testing, reproducible builds, and storing symbol graph output in text-diff-able environments like Git repositories. We should investigate what it would take to force an ordering for symbols and relationships in the symbol graph.