Add guide for adding gestures to components

[jelbourn]

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With Angular v9, we removed direct gesture handling in Angular Material. We did this for a number of reasons, including:

• Drop dependency on mostly unmaintained HammerJS
• Give people flexibility to use other gesture solutions
• No requirement to add gesture code for users that don't actually want it
• Simplify project setup

However, we should still have a guide that explains how to add gestures for users that want them. The guide should cover topics including:

• Swiping out a sidenav
• Swiping between tabs
• Swiping items away on a list / table
• Swiping calendar months

Related to #2209