coprocessor: Refactor encoding TiDBColumn

[JaySon-Huang]

What problem does this PR solve?

Issue Number: ref #9032

Problem Summary:

TiDBColumn::data and TiDBColumn::finishAppendVar should not be exposed as public

What is changed and how it works?

• Add TiDBColumn::appendVectorF32 and ColumnArray::getElementRef to replace the origin implementation
• Use encodeLittleEndian in TiDBColumn::appendVectorF32 instead of exception checking

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

None

[Lloyd-Pottiger]

lgtm

[breezewish]

Nice change!

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: breezewish, Lloyd-Pottiger

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-08-01 07:07:56.013931209 +0000 UTC m=+425992.293979276: ☑️ agreed by Lloyd-Pottiger.
• 2024-08-01 07:20:32.951653126 +0000 UTC m=+426749.231701191: ☑️ agreed by breezewish.