Invalid d.ts produced after 0.2.56 upgrade

[TomCrypto]

Describe the Bug

After upgrading to 0.2.56, there are errors in the generated crate.d.ts (not the _bg one) that are due to invalid generated typescript.

Steps to Reproduce

1. Use the https://github.com/rustwasm/wasm-pack-template or whatever to create a new project
2. Insert the following test case

#[wasm_bindgen]
pub struct Foo {}

#[wasm_bindgen]
impl Foo {
    pub fn test1(&mut self) -> bool {
        true
    }

    pub fn test2(&mut self, _foo: f32) {
        return;
    }
}

Expected Behavior

The expected (and generated as of 0.2.55) d.ts looked like this:

export class Foo {
  free(): void;
/**
* @returns {boolean} 
*/
  test1(): boolean;
/**
* @param {number} _foo 
*/
  test2(_foo: number): void;
}

Actual Behavior

When using wasm-bindgen 0.2.56 instead, the following invalid typescript is generated instead:

export class Foo {
  free(): void;
/**
* @returns {bool} 
*/
  test1(): bool;
/**
* @param {number} this.ptr 
*/
  test2(this.ptr: number): void;
}

Additional Context

There might be other regressions; these are just the ones that I immediately found in my wasm project.

[alexcrichton]

Thanks for the report here! Indeed bool -> boolean was one glaring error, and I can see where the other is coming from (the this.ptr weirdness), I'll try to work on a fix soon!