*: Introduce TemporaryTableDDL to provide unified APIs for temporary table ddl operations

[lcwangchao]

What problem does this PR solve?

Issue Number: close #27775

Problem Summary:

We have too many temporary table states in session.variables and they are exposed to users directly. For example, when dropping a local temporary table, the ddl executor should invoke sessVars.LocalTemporaryTables.RemoveTable first and then clear the table's data in sessVars.TemporaryTableData.

To decouple those codes, we should introduce a package to manage these operations and provide unified APIs. For the ddl operations this pr introduces a new interface TemporaryTableDDL to do the ddl things. It hides detail states in session.variable and the users should not care about it.

The defination of TemporaryTableDDL is:

type TemporaryTableDDL interface {
	CreateLocalTemporaryTable(schema model.CIStr, info *model.TableInfo) error
	DropLocalTemporaryTable(schema model.CIStr, tblName model.CIStr) error
	TruncateLocalTemporaryTable(schema model.CIStr, tblName model.CIStr) error
}

The current pr only provides some ddl APIs. More works will be done in later prs.

The pr is also required by #26952 to provide some methods to custom snapshot retrievers. You can see the draft here: #26948

What is changed and how it works?

Introduce TemporaryTableDDL to provide unified APIs for temporary table ddl operations

Check List

Tests

• Unit test

Release note

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• djshow832
• tiancaiamao

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[lcwangchao]

/run-check_dev_2

[djshow832]

/merge

[ti-chi-bot]

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

Commit hash: 12e035c

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