sessionctx: support encoding and decoding prepared statements

[djshow832]

What problem does this PR solve?

Issue Number: close #35689

Problem Summary:
support encoding and decoding prepared statements

What is changed and how it works?

• Register TiDBContext to session.sessionStatesHandlers to handle the encoding and decoding of prepared statements.
• Encode and decode prepared statements in TiDBContext.
• Remove TiDBContext.currentDB because it's not used now.

Notice:

• The prepared statement cannot be decoded if the table is dropped / current db is dropped / privilege is updated / sql_mode is updated after preparing. I filed another issue for this: lazily replaying prepared statements for session manager #35806. I'll address it in another PR with a lower priority.
• I have added test cases for the scenarios above, except for the privilege, because I found another privilege bug of prepared statements: Privilege check is skipped for PREPARE statement #35784.
• Encoding prepared statements should report an error when the statement is waiting for COM_STMT_EXECUTE (after COM_STMT_SEND_LONG_DATA) or COM_STMT_FETCH (in useCursor mode). I'll do it in another PR.
• Metrics / slow log / statements_summary / audit log should not record the PREPARE statement when it's replayed. I'll check it in the future, with a lower priority.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• bb7133
• xhebox

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[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/c916d8f40e36c1d70dbb3a9b035a652c4fc900bf

[xhebox]

LGTM

[bb7133]

LGTM

[bb7133]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 78acb63

[sre-bot]

TiDB MergeCI notify

🔴 Bad News! New failing [1] after this pr merged.
These new failed integration tests seem to be caused by the current PR, please try to fix these new failed integration tests, thanks!

CI Name	Result	Duration	Compare with Parent commit
idc-jenkins-ci-tidb/integration-common-test	🟥 failed 1, success 10, total 11	17 min	New failing
idc-jenkins-ci/integration-cdc-test	🟢 all 35 tests passed	23 min	Existing passed
idc-jenkins-ci-tidb/common-test	🟢 all 12 tests passed	10 min	Existing passed
idc-jenkins-ci-tidb/tics-test	🟢 all 1 tests passed	5 min 53 sec	Existing passed
idc-jenkins-ci-tidb/integration-ddl-test	🟢 all 6 tests passed	5 min 41 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-2	🟢 all 28 tests passed	5 min 38 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-1	🟢 all 26 tests passed	4 min 51 sec	Existing passed
idc-jenkins-ci-tidb/mybatis-test	🟢 all 1 tests passed	3 min 2 sec	Existing passed
idc-jenkins-ci-tidb/integration-compatibility-test	🟢 all 1 tests passed	2 min 41 sec	Existing passed
idc-jenkins-ci-tidb/plugin-test	🟢 build success, plugin test success	4min	Existing passed