lsp tracing: support changing deno.tracing config while lsp is running

[nathanwhit]

Right now if you change the tracing config, you have to restart the LSP for the changes to take effect.

I originally tried this, but there's some bug when setting the tracing subscriber as a thread local default (as opposed to global) that causes spans to lose their parents. It may be an issue with the otel exporter, but not sure.

cc #27843