fix($injector): ensure $get method invoked with provider context

0d3b69a5f27b41745b504c7ffd8d72653bac1f85 broke this by calling $get with an undefined
context, which in strict mode would be undefined. This fixes this by ensuring that the
provider is used as the context, as it was originally.

Closes #9511
Closes #9512
chore(injectorSpec.js): make jshint happy

...oops ._.
WIP - feat($anchorScroll): add support for configurable scroll offset

Add support for a configurable scroll offset to $anchorScrollProvider.
The offset is expressed in pixels and can be specified either as a fixed
value or as a function that return the offset it pixels dynamically.
(This is a POC and a WIP: no docs, no tests)

Related to #9368

Closes #2070, #9360
WIP: simplify $anchorScroll offset feature
WIP - feat($anchorScroll): add docs and tests and make small improvements

Finalize the implementation, fix scrolling for elements near the end of
the page, make sure the values calculated for top-offset and height are
accurate (and unaffected by box-sizing or offset-parents).
Separately document $anchorScrollProvider, document the newly added
`yOffset` property of $anchorScroll, fix minor issues in the examples and
overall improve the docs.
Add tests for `$anchorScroll.yOffset` and make some necessary
modifications to the existing test helper functions.