fix(label): set the ios variables to null to avoid styling

fixes ionic-team#11631

docs(alert): imported AlertController in usage example (ionic-team#11567

)

Added an importation for use the alert controller on line 52.

fix(select): incorrect assert condition

fix(searchbar): input is debounced

fix(inputs): ionChange is fired after updating ngModel

test(menu): update directory structure for menu/multiple

fix(scroll-view): do not set initialized until it is enabled (ionic-t…

…eam#10817)

regression caused by 7e9bad5

test(toolbar): fix model header

chore(deps): revert angular version

chore(contributing): tweak info and bullet points