Add primary_clicked & secondary_clicked for PointerState.

[aleokdev]

Is your feature request related to a problem? Please describe.
I'd like to detect if the user clicked something with the primary button somewhere in order to cancel their selection.
While we have .any_click() and .primary_down(), we don't have .primary_clicked()!

Describe the solution you'd like
I'd like a way to know if one button was clicked on this frame.

Describe alternatives you've considered
Using .any_click() && .primary_down(), but this is faulty: The user could be holding down the primary button and then have clicked with another button.

[emilk]

Sounds good, please make a PR adding the missing methods!