All hooks receive a `TyCtxtAt` argument.
Currently hooks can be called through `TyCtxtAt` or `TyCtxt`. In the
latter case, a `TyCtxtAt` is constructed with a dummy span and passed to
the hook.
However, in practice hooks are never called through `TyCtxtAt`, and
always receive a dummy span. (I confirmed this via code inspection, and
double-checked it by temporarily making the `TyCtxtAt` code path panic
and running all the tests.)
This commit removes all the `TyCtxtAt` machinery for hooks. All hooks
now receive `TyCtxt` instead of `TyCtxtAt`. There are two existing hooks
that use `TyCtxtAt::span`: `const_caller_location_provider` and
`try_destructure_mir_constant_for_user_output`. For both hooks the span
is always a dummy span, probably unintentionally. This dummy span use is
now explicit. If a non-dummy span is needed for these two hooks it would
be easy to add it as an extra argument because hooks are less
constrained than queries.
Outline default query and hook provider function implementations
The default query and hook provider functions call `bug!` with a decently long message.
Due to argument inlining in `format_args!` ([`flatten_format_args`](https://github.com/rust-lang/rust/issues/78356)), this ends up duplicating the message for each query, adding ~90KB to `librustc_driver.so` of unreachable panic messages.
To avoid this, we can outline the common `bug!` logic.
This will allow MIR building to check whether a function is eligible for
coverage instrumentation, and avoid collecting branch coverage info if it is
not.
