The idea here is that the crate graph may change over time, but library source file contents *never* will (or really never should). Disconnecting the two means that queries that depend on library sources will not need to re-validatewhen the crate graph changes (unless they depend on the crate graph in some capacity).
When viewing traces, it's slightly confusing when the span name doesn't
match the function name. Ensure the names are consistent.
(It might be worth moving most of these to use #[tracing::instrument]
so the name can never go stale. @davidbarsky suggested that is marginally
slower, so I've just done the simple change here.)
This commit also adds `tracing` to NotificationDispatcher/RequestDispatcher,
bumps `rust-analyzer-salsa` to 0.17.0-pre.6, `always-assert` to 0.2, and
removes the homegrown `hprof` implementation in favor of a vendored
tracing-span-tree.
