This wasn't a right decision in the first place, the feature flag was
broken in the last rustfmt release, and syntax highlighting of imports
is more important anyway
Can be used like this:
```
$ cargo run --release -p ra_cli -- \
analysis-bench ../chalk/ \
--complete ../chalk/chalk-engine/src/logic.rs:94:0
loading: 225.970093ms
from scratch: 8.492373325s
no change: 445.265µs
trivial change: 95.631242ms
```
Or like this:
```
$ cargo run --release -p ra_cli -- \
analysis-bench ../chalk/ \
--highlight ../chalk/chalk-engine/src/logic.rs
loading: 209.873484ms
from scratch: 9.504916942s
no change: 7.731119ms
trivial change: 124.984039ms
```
"from scratch" includes initial analysis of the relevant bits of the
project
"no change" just asks the same question for the second time. It
measures overhead on assembling the answer outside of salsa.
"trivial change" doesn't do an actual salsa change, it just advances
the revision. This test how fast is salsa at validating things.
This makes it more like the other code model types.
Also make Module::definition_source/declaration_source return HirFileIds, to
make them more like the other source functions.
