Enable Weak References by default

[luveti]

Motivation

WeakRef is now supported by all mainstream browsers: https://caniuse.com/mdn-javascript_builtins_weakref

Proposed Solution

Remove WASM_BINDGEN_WEAKREF and set the default value to true.

Alternatives

Leak memory forever.. :)

Additional Context

N/A

[daxpedda]

Both reference types and multi-value are finished proposals and stable on all browsers for a long time now.

Multi-value is a bit more involved because it requires compiler support, which is currently broken anyway, but at least reference types can be enabled by default next to weak references too.

[daxpedda]

Apparently there are runtimes, e.g. serverless, that don't support weak references. So I'm not sure if we can enable this by default without a breaking change.

[pheki]

Could we use feature detection for WeakRef? Then we would avoid breaking old browsers and serverless while making it available to most browsers

[daxpedda]

I never looked into what wasm-bindgen-cli does here exactly, but that's probably the best solution here.
Happy to review a PR for that.

[luxalpa]

It seems this got fixed in 0.2.91? Can this be confirmed?
#3812
#3822

[Liamolucko]

It seems this got fixed in 0.2.91? Can this be confirmed?

#3812

#3822

Yes, except that it has a pretty severe flaw right now: #3854.

#3854 is the correct place to track that though, not here, so I'll close it.