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

#### 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

Start by locating the matTooltip implementation and its existing accessibility behavior. Check how it applies aria-describedby to hosts, then define the supported aria-labelledby configuration and verify that tooltip labeling works for unlabeled buttons without regressing description behavior.

Written by the indexing model from the issue text.