docs: fix wrong gesture_input path

[yanceyou]

Description

Modify to the real path 'package:flame/gestures.dart' => 'package:flame/src/gestures/detectors.dart'

Checklist

• I have followed the Contributor Guide when preparing my PR.
• I have updated/added tests for ALL new/updated/fixed functionality.
• I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• I have updated/added relevant examples in examples or docs.

Breaking Change?

• Yes, this PR is a breaking change.
• No, this PR is not a breaking change.

Related Issues

[yanceyou]

Not entirely correct, the MultiTouchTapDetector and MultiTouchDragDetector are found in 'package:flame/src/events/game_mixins/*', closed.