[3.11] gh-114955: Add clear to MutableSequence's mixin methods in document (gh-114956) (#114962)

gh-114955: Add clear to MutableSequence's mixin methods in document (gh-114956)
(cherry picked from commit b4240fd68ecd2c22ec82ac549eabfe5fd35fab2a)

Co-authored-by: AN Long <aisk@users.noreply.github.com>