Site and AppRunner

[asvetlov]

I'm trying to cleanup infrastructure for web application runners.

The PR introduces a site and AppRunner concepts.

Fixes #2121 and #2375
Supersedes #2465

The work is still not finished yet but I believe my intention is clear.

[samuelcolvin]

Can you give an example of how this would work and how it's better than the current situation?

[asvetlov]

run_app functionality could be implemented like

runner = AppRunner(app)
await runner.initialize()  # setup app loop and run `on_startup()` signal.
site = HTTPSite(runner, 'localhost', 8000)
await site.start()
sslsite = HTTPSite(runner, 'localhost', 8443, ssl_context=....)
await sslsite.start()
# wait for closing
await runner.finalize()  # close sites, call app.cleanup()

[asvetlov]

web.run_app() is fully reimplemented on top of AppRunner and sites.
Working on 100% test coverage and docs.

[codecov-io]

Codecov Report

Merging #2530 into master will increase coverage by 0.08%.
The diff coverage is 99.13%.

@@            Coverage Diff             @@
##           master    #2530      +/-   ##
==========================================
+ Coverage   97.78%   97.87%   +0.08%     
==========================================
  Files          36       38       +2     
  Lines        7236     7305      +69     
  Branches     1262     1263       +1     
==========================================
+ Hits         7076     7150      +74     
+ Misses         55       51       -4     
+ Partials      105      104       -1

Impacted Files	Coverage Δ
aiohttp/web.py	98.76% <100%> (+0.18%)	⬆️
aiohttp/web_site.py	100% <100%> (ø)
aiohttp/worker.py	99.04% <95.65%> (+2.92%)	⬆️
aiohttp/web_app.py	98.81% <98.81%> (ø)

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[asvetlov]

I'm going to merge the PR.

Documentation is needed but I'll do it in separate PR.
Implementation affects many files, better to merge it quickly to avoid permanent code divergency and merge conflicts,

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a [new issue] for related bugs.
If you feel like there's important points made in this discussion, please include those exceprts into that [new issue].
[new issue]: https://github.com/aio-libs/aiohttp/issues/new