Ember Core - H2Server - Split for comprehension

[diesalbla]

Redo of #6525 in a series of commits, to make each change obvious, to attend @armanbilge
comment in #6523 (comment)

Each commit is easier to review, specially if hiding whitespace changes.

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In the ember-core package, in the H2Server, the fromSocket method,
we refactor the code to split the main expression, a for comprehension
in Resource, to extract a couple of methods in F:

• Initialising the H2Connection itself.
• Clear closed streams from the map of streams.
• Process a created stream, which includes handling push promises.

This is similar to recent PR #6523, and follows on previous PRs like #6425.

Note: Half of line changes are whitespace-only.

[armanbilge]

Thanks, this is great. Very easy to follow :) thanks for refactoring.