bug(matTooltip): Add option to set aria-labelledby rather than aria-describedby

[kseamon]

Reproduction

matTooltip is only able to apply aria-describedby to its host element. This is not optimal for host elements that have no aria-label or text contents.

Expected Behavior

What behavior were you expecting to see?

For a button with no textual label, eg a MatIconButton, a tooltip typically provides a label rather than a description. Having matTooltip apply aria-labeledby rather than would be better in these cases.

At the very least, it would be good to have an Input to configure matTooltip's labeledby vs describedby preference. Extra credit: change the default for obvious cases like MatIconButton.

Actual Behavior

What behavior did you actually see?

matTooltip applies aria-describedby, with no option to change this behavior.

Environment

• Angular: 12
• CDK/Material: 12
• Browser(s): any
• Operating System (e.g. Windows, macOS, Ubuntu): any