infoschema: fix exec_count of prepared statements in statement summary (#17064)

[sre-bot]

cherry-pick #17064 to release-4.0

---

What problem does this PR solve?

Problem Summary:

mysql> prepare stmt from 'select ?';
Query OK, 0 rows affected (0.00 sec)

mysql> set @number=1;
Query OK, 0 rows affected (0.00 sec)

mysql> execute stmt using @number;
+------+
| ?    |
+------+
| 1    |
+------+
1 row in set (0.00 sec)

mysql> select exec_count from information_schema.statements_summary where digest_text='select ?';
+------------+
| exec_count |
+------------+
|          2 |
+------------+
1 row in set (0.00 sec)

The final result should be 1, not 2.

Note: In events_statements_summary_by_digest in MySQL, PREPARE and EXECUTE statements are recorded separately, and digest_text stays what they were.
But we record the SQL filled with parameters (referred as final SQL below), because:

1. Slow queries use the digest of the final SQL, and Dashboard use the digest to jump from statements to slow query. So the digests should be the same.
2. It's easier to filter statements by stmt_type field.
3. query_sample_text can be the final SQL, which can be used to reproduce the problem more easily.

What is changed and how it works?

What's Changed:
Ignore PREPARE statements in statement summary.

Related changes

• Need to cherry-pick to the release branch

Check List

Tests

• Unit test

Side effects

N/A

Release note

• fix exec_count of prepared statements in statement summary.

[sre-bot]

/run-all-tests

[Deardrops]

LGTM

[AilinKid]

LGTM

[AilinKid]

/run-all-tests

[djshow832]

/run-all-tests

[djshow832]

UT failed due to #16870

[djshow832]

/run-all-tests