Fixes #19737 by adding brotli compression parameters.
Time after:
`Accept-Encoding: gzip`:
```
real 0m0.214s
user 0m0.005s
sys 0m0.013s
```
`Accept-Encoding: br`:
Before:
```
real 0m10.303s
user 0m0.005s
sys 0m0.010s
```
After:
```
real 0m0.127s
user 0m0.006s
sys 0m0.014s
```
Fixes for various `Attemped to access invalid request` bugs (#19058,
#15427, #17213).
We did not wait for both a drop event and a completion event before
removing items from the slab table. This ensures that we do so.
In addition, the slab methods are refactored out into `slab.rs` for
maintainability.
`Content-Encoding: gzip` support for `Deno.serve`. This doesn't support
Brotli (`br`) yet, however it should not be difficult to add. Heuristics
for compression are modelled after those in `Deno.serveHttp`.
Tests are provided to ensure that the gzip compression is correct. We
chunk a number of different streams (zeros, hard-to-compress data,
already-gzipped data) in a number of different ways (regular, random,
large/small, small/large).
This is a rewrite of the `Deno.serve` API to live on top of hyper
1.0-rc3. The code should be more maintainable long-term, and avoids some
of the slower mpsc patterns that made the older code less efficient than
it could have been.
Missing features:
- `upgradeHttp` and `upgradeHttpRaw` (`upgradeWebSocket` is available,
however).
- Automatic compression is unavailable on responses.
