Specify result type of `ConstraintSchemaInterface::getTableIndexes()` method to `IndexConstraint[]`

[vjik]

Q	A
Is bugfix?	❌
New feature?	❌
Breaks BC?	❌
Fixed issues	-

[what-the-diff[bot]]

PR Summary

• Enhancement to the ConstraintSchemaInterface::getTableIndexes() method This PR adds an enhancement that updates the result type of the getTableIndexes() method in ConstraintSchemaInterface from a more general “array” type to the specific IndexConstraint[]. This modification enhances the precision of the data type, ensuring that the function only returns IndexConstraint elements.

• Removal of unused code in AbstractSchema::getTableIndexes() We have removed certain pieces of code from the getTableIndexes() method in AbstractSchema, enhancing code cleanliness and making the function more efficient by eliminating code that was not being used.

• Removal of an unnecessary import in AbstractDMLQueryBuilder This PR also includes a cleanup change that removes an unnecessary import of Yiisoft\Db\Constraint\IndexConstraint in the AbstractDMLQueryBuilder. This helps to reduce clutter and maintain neatness in our codebase.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (8a3d81f) 99.64% compared to head (b3be66b) 99.64%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #784 +/- ## ============================================ - Coverage 99.64% 99.64% -0.01% + Complexity 1272 1271 -1 ============================================ Files 63 63 Lines 3061 3060 -1 ============================================ - Hits 3050 3049 -1 Misses 11 11 ```

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