…hat) on asymmetrically sized sets and extend unit tests slightly beyond that

Also, don't suggest comparing to zero for non-numeric expressions.

It shouldn't matter, but hey - better safe than sorry!

Fix poor worst case performance of set intersection

Specifically, intersection of asymmetrically sized sets when the large set is on the left. See also the [latest answer on stackoverflow](https://stackoverflow.com/questions/35439376/python-set-intersection-is-faster-then-rust-hashset-intersection).

Also applied to the union member, where the effect is much less but still measurable.

Formatted the changed code only, does not increase the error count reported by tidy check, and tried to adhere to the spirit of the unit tests.

Clean up and fix a bug in query plumbing

r? @michaelwoerister

provide suggestion for invalid boolean cast

Also, don't suggest comparing to zero for non-numeric expressions.

Modify some parser diagnostics to continue evaluating beyond the parser

Continue evaluating further errors after parser errors on:
 - trailing type argument attribute
 - lifetime in incorrect location
 - incorrect binary literal
 - missing `for` in `impl Trait for Foo`
 - type argument in `where` clause
 - incorrect float literal
 - incorrect `..` in pattern
 - associated types
 - incorrect discriminator value variant error

and others. All of these were found by making `continue-parse-after-error` `true` by default to identify errors that would need few changes. There are now only a handful of errors that have any change with `continue-parse-after-error` enabled.

These changes make it so `rust` _won't_ stop evaluation after finishing parsing, enabling type checking errors to be displayed on the existing code without having to fix the parse errors.

Each commit has an individual diagnostic change with their corresponding tests.

CC #48724.

Querify local `plugin_registrar_fn` and `proc_macro_decls_static`

Instead of calculating them as part of the `Session`, we do that in the query system.
It's also nice that these queries are already defined for external crates - here, we provide the queries for the local crate.

r? @nikomatsakis

Unaccept `extern_in_paths`

Based on completed fcp-close in #55600, this removes `extern_in_path` (e.g. `extern::foo::bar`) from the language. The changes are primarily reversing 32db83b.

Closes #55600

r? @petrochenkov

Recover from item trailing semicolon

CC rust-lang/rfcs#2479

r? @petrochenkov

…chton

Add a debug_assert to Vec::set_len

Following the precedent of #52972, which found llogiq/bytecount#42.

(This may well make a test fail; let's see what Travis says.)

Rollup of 8 pull requests

Successful merges:

 - #57043 (Fix poor worst case performance of set intersection)
 - #57480 (Clean up and fix a bug in query plumbing)
 - #57481 (provide suggestion for invalid boolean cast)
 - #57540 (Modify some parser diagnostics to continue evaluating beyond the parser)
 - #57570 (Querify local `plugin_registrar_fn` and `proc_macro_decls_static`)
 - #57572 (Unaccept `extern_in_paths`)
 - #57585 (Recover from item trailing semicolon)
 - #57589 (Add a debug_assert to Vec::set_len)

Failed merges:

r? @ghost