docs(guide/e2e-testing): fix typos
docs(numberFilter): fix explanation of default fraction size

The default fraction size for the number filter is actually computed
from the `NUMBER_FORMATS.PATTERNS.maxFrac` value in the current locale.

Closes #3157
docs(ngModelController): provide a more intuitive example

The example directive, using contenteditable was not showing required
even if you cleared the content from it.

Closes #3156
docs(angular.identity): fix missing 'angular' in identity function
docs(ngMock): correct verifyNoOutstandingExpectation example