server: support decoding prepared string args to character_set_client(#30723)

[tangenta]

Cherry-pick #30723 to release-5.3-20211223.

[ti-chi-bot]

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[ti-chi-bot]

@tangenta: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

To merge this cherry pick, it must first be approved by the collaborators.

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[zhouqiang-cl]

/run-build-arm64 comment=true

[sre-bot]

download tidb binary(linux arm64) at http://fileserver.pingcap.net/download/builds/pingcap/test/tidb/f62a02a921b1917771e2888daab1831dd4232878/centos7/tidb-linux-arm64.tar.gz

[bb7133]

/run-check_dev

[bb7133]

LGTM