Documentation update for Timer class
Documentation update for Timer class

Example updated and new ones added.

Closes https://github.com/dart-lang/sdk/pull/47931
https://github.com/dart-lang/sdk/pull/47931

GitOrigin-RevId: 5486bd82e5e3545bee5f04dbb5fc6120a1425041
Change-Id: I2ffe2053fbc54aad2fae27220e48dfac70d5aa63
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/224180
Reviewed-by: Lasse Nielsen <80295e4ef244a07779f93eaa95d582bad8e316a5@google.com>
Commit-Queue: Lasse Nielsen <80295e4ef244a07779f93eaa95d582bad8e316a5@google.com>

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