Don't create a new resource with allow_head=True

[asvetlov]

Backward incompatible but I believe almost nobody is affected.

[kxepal]

I guess it's improvement, not removal.

[asvetlov]

It's both optimization and breaking change: in aiohttp 2.x the call router.add_get('/', handler, name='name') adds two named resources: name for GET and name-head for HEAD.
But both resources are identical.

After PR merging I want add generic optimization for sequential add_route() calls if created resource is the same.

router.add_get('/', ...)
router.add_post('/', ...)

should create the single resource if path and name are the same.

[codecov-io]

Codecov Report

Merging #2585 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #2585   +/-   ##
=======================================
  Coverage   97.71%   97.71%           
=======================================
  Files          36       36           
  Lines        7229     7229           
  Branches     1262     1262           
=======================================
  Hits         7064     7064           
  Misses         58       58           
  Partials      107      107

Impacted Files	Coverage Δ
aiohttp/web_urldispatcher.py	99.49% <100%> (ø)	⬆️

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[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