Join two independent ops into one. A fast impl of one + a slow callback
of another. Here's an example showing optimized paths for latin-1 via
fast call and the next-best fallback using V8 apis.
```rust
#[op(v8)]
fn op_encoding_encode_into_fallback(
scope: &mut v8::HandleScope,
input: serde_v8::Value,
// ...
#[op(fast, slow = op_encoding_encode_into_fallback)]
fn op_encoding_encode_into(
input: Cow<'_, str>,
// ...
```
Benchmark results of the fallback path:
```
time target/release/deno run -A --unstable ./cli/tests/testdata/benches/text_encoder_into_perf.js
________________________________________________________
Executed in 70.90 millis fish external
usr time 57.76 millis 0.23 millis 57.53 millis
sys time 17.02 millis 1.28 millis 15.74 millis
target/release/deno_main run -A --unstable ./cli/tests/testdata/benches/text_encoder_into_perf.js
________________________________________________________
Executed in 154.00 millis fish external
usr time 67.14 millis 0.26 millis 66.88 millis
sys time 38.82 millis 1.47 millis 37.35 millis
```
This PR introduces Wasm ops. These calls are optimized for entry from
Wasm land.
The `#[op(wasm)]` attribute is opt-in.
Last parameter `Option<&mut [u8]>` is the memory slice of the Wasm
module *when entered from a Fast API call*. Otherwise, the user is
expected to implement logic to obtain the memory if `None`
```rust
#[op(wasm)]
pub fn op_args_get(
offset: i32,
buffer_offset: i32,
memory: Option<&mut [u8]>,
) {
// ...
}
```
