feat(ext/web): use readableStreamDefaultReaderRead in resourceForReadableStream

[mmastrac]

We can go one level down in abstraction and avoid using the public ReadableStream APIs.

This patch ~5% perf boost on small ReadableStream:

Running 10s test @ http://localhost:8080/
  2 threads and 10 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency   148.32us  108.95us   3.88ms   95.71%
    Req/Sec    33.24k     2.68k   37.94k    73.76%
  668188 requests in 10.10s, 77.74MB read
Requests/sec:  66162.91
Transfer/sec:      7.70MB

main:

Running 10s test @ http://localhost:8080/
  2 threads and 10 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency   150.23us   67.61us   4.39ms   94.80%
    Req/Sec    31.81k     1.55k   35.56k    83.17%
  639078 requests in 10.10s, 74.36MB read
Requests/sec:  63273.72
Transfer/sec:      7.36MB

[bartlomieju]

LGTM