Move RepoUniverseSymbolJob to package zoekt, rename job, and add tracing

Created by: tbliu98

Part of #34009 (closed)

Since RepoUniverseSymbolSearchJob runs a global symbol search via Zoekt, it seems more appropriate for it to live in the zoekt package alongside ZoektSymbolSearchJob.

This PR:

• Moves RepoUniverseSymbolSearchJob into symbol_search_job.go alongside ZoektSymbolSearchJob
• Renames RepoUniverseSymbolSearchJob to ZoektGlobalSymbolSearchJob
• Adds trace tags to ZoektGlobalSymbolSearchJob
• Renames symbol_search_job.go to symbol_search.go

Test plan

Manually verify that ZoektGlobalSymbolSearchJob is still constructed & run when expected and that behavior is the same. Visually verify trace output.