mounter(ticdc): mount float32 value correctly to avoid the precision lost. (#8502)

[ti-chi-bot]

This is an automated cherry-pick of #8502

What problem does this PR solve?

Issue Number: close #8490

What is changed and how it works?

• For float32 types, fetch it from thedatum by use the corresponding method.

Check List

Tests

• Unit test

Questions

Will it cause performance regression or break compatibility?

Do you need to update user documentation, design documentation or monitoring documentation?

Release note

Fix float32 types precision lost

[ti-chi-bot]

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[ti-chi-bot]

@ti-chi-bot: 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.

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[ti-chi-bot]

@ti-chi-bot: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-cdc-integration-kafka-test	15d7504	link	true	/test cdc-integration-kafka-test
jenkins-ticdc/verify	15d7504	link	true	/test verify
pull-cdc-integration-mysql-test	15d7504	link	true	/test cdc-integration-mysql-test

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[ti-chi-bot]

@ti-chi-bot: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
jenkins-ticdc/verify	15d7504	link	true	/test verify
pull-cdc-integration-mysql-test	15d7504	link	true	/test cdc-integration-mysql-test

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository. I understand the commands that are listed here.