web: Bump wasm-bindgen to 0.2.78

As usual, also bump its helper crates (`js-sys`, `wasm-bindgen-futures`)
to the latest versions, except for `web-sys` which is locked by wgpu
to 0.3.50.

avm2: implement bkpt, bkptline, timestamp as no-ops

avm1: Simplify `Value::abstract_lt`

* Change its return type to `Option<bool>`.
* Use Rust's `f64::partial_cmp` to compare two numbers, which should
be more efficient.

web: Indent using spaces in tsconfig.json

chore: Bump TypeScript config to es2017

web: support no trailing slash in base parameter

web: don't panic if failing to create an audio buffer

chore: Bump to wasm-bindgen 0.2.77

web: Support salign, quality, & scale embed/object attributes (part of …

…ruffle-rs#4258)

web: check array_buffer promise for failure