HttpStreamPool: Refactor NotifyStreamReady()

This is a preparation for introducing "draining" state to AttemptManager
(https://crrev.com/c/6535041). NotifyStreamReady() contained HTTP/1.1
(or older version) specific logic that put a created HttpStream back to
the group (pool) when there was no Job to notify. Move HTTP/1.1 specific
logic to CreateTextBasedStreamAndNotify() so that the method won't have
a weird logic when we introduce the "draining" state.

Bug: 416088643, 414173943
Change-Id: I565385c2e1f55867a1872ac4f561f95c3c076ada
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6535141
Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
Reviewed-by: mmenke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1459212}