docs($location): fix method-name and typos in `ihshprfx` error

Closes #10106
fix($http): return empty headers, ignore properties in Object prototype

Fix response headers with an empty value Empty response header values are legal
(http://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html).

The headers getter fn will now only return null if the header property is not an own property.

Closes #7779
Closes #10113
Closes #10091
feat(ngPluralize): add support for `count` to be a one-time expression

Closes #10004