Support expr when use typescript_custom_section attribute

[swnb]

for example

#[wasm_bindgen(typescript_custom_section)]
const _: &'static str = include_str!("./types.d.ts");

const TS_INTERFACE_EXPORT: &str = "interface Person2 { height: number; }";
#[wasm_bindgen(typescript_custom_section)]
const _: &str = TS_INTERFACE_EXPORT;

this pr is inspired by #3308 , and will fix [#2828]

this pr is compatible with current encode logic, so wasm-bindgen cli can decode normally without updating

[swnb]

I don't mean to rush you , but any progress about this pr @daxpedda

[daxpedda]

Unfortunately I'm not really qualified to review any TS related stuff, so I leave it to other maintainers.

[Liamolucko]

Thanks!

Could you add a changelog entry?

[swnb]

Thanks for your patience, I've updated the changelog