Dramatically improving the build time of web-sys (#2012)

* Pre-generating web-sys

* Fixing build errors

* Minor refactor for the unit tests

* Changing to generate #[wasm_bindgen} annotations

* Fixing code generation

* Adding in main bin to wasm-bindgen-webidl

* Fixing more problems

* Adding in support for unstable APIs

* Fixing bug with code generation

* More code generation fixes

* Improving the webidl program

* Removing unnecessary cfg from the generated code

* Splitting doc comments onto separate lines

* Improving the generation for unstable features

* Adding in support for string values in enums

* Now runs rustfmt on the mod.rs file

* Fixing codegen for constructors

* Fixing webidl-tests

* Fixing build errors

* Another fix for build errors

* Renaming typescript_name to typescript_type

* Adding in docs for typescript_type

* Adding in CI script to verify that web-sys is up to date

* Fixing CI script

* Fixing CI script

* Don't suppress git diff output

* Remove duplicate definitions of `Location`

Looks to be a preexisting bug in wasm-bindgen?

* Regenerate webidl

* Try to get the git diff command right

* Handle named constructors in WebIDL

* Remove stray rustfmt.toml

* Add back NamedConstructorBar definition in tests

* Run stable rustfmt over everything

* Don't run Cargo in a build script

Instead refactor things so webidl-tests can use the Rust-code-generation
as a library in a build script. Also fixes `cargo fmt` in the
repository.

* Fixup generated code

* Running web-sys checks on stable

* Improving the code generation a little

* Running rustfmt

Co-authored-by: Alex Crichton <alex@alexcrichton.com>

crates/macro/ui-tests/invalid-enums.stderr

@@ -1,4 +1,4 @@
-error: only public enums are allowed with #[wasm_bindgen]
+error: cannot export empty enums to JS
  --> $DIR/invalid-enums.rs:4:1
   |
 4 | enum A {}

crates/macro/ui-tests/invalid-imports.stderr

@@ -22,18 +22,6 @@ error: first argument of method must be a path
 14 |     fn f3(x: &&u32);
    |              ^^^^^
 
-error: multi-segment paths are not supported yet
-  --> $DIR/invalid-imports.rs:16:15
-   |
-16 |     fn f4(x: &foo::Bar);
-   |               ^^^^^^^^
-
-error: global paths are not supported yet
-  --> $DIR/invalid-imports.rs:18:15
-   |
-18 |     fn f4(x: &::Bar);
-   |               ^^^^^
-
 error: paths with type parameters are not supported yet
   --> $DIR/invalid-imports.rs:20:15
    |
@@ -52,12 +40,6 @@ error: constructor returns must be bare types
 25 |     fn f();
    |     ^^^^^^^
 
-error: global paths are not supported yet
-  --> $DIR/invalid-imports.rs:27:15
-   |
-27 |     fn f() -> ::Bar;
-   |               ^^^^^
-
 error: return value of constructor must be a bare path
   --> $DIR/invalid-imports.rs:29:5
    |