planner: support pushing down predicates to memory tables in prepared mode (#40262)

[ti-chi-bot]

This is an automated cherry-pick of #40262

What problem does this PR solve?

Issue Number: close #39605

Problem Summary:
Predicates are not pushed down to memory tables in the prepared mode because the author avoids doing that intentionally. I'm not sure why but it should work.

What is changed and how it works?

Get the value from constant when it uses prepared mode. Note that it still skips evaluating when DeferredExpr is not nil.

Check List

Tests

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

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

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

Optimize the memory when querying from memory tables with predicates in prepared statements

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-06-14 02:58:57.009865437 +0000 UTC m=+140933.424469515: ☑️ agreed by rleungx.
• 2023-06-14 04:02:55.283962365 +0000 UTC m=+144771.698566444: ☑️ agreed by xhebox.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: mjonss, rleungx, xhebox

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