fix: allow implicit cast of numbers literals to decimals on insert/select

[spena]

Description

Fixes #5285

Allows implicitly casting of numeric literals to decimals when executing an INSERT/SELECT statement. A conversion from one literal type to another is done in the SelectionUtil.buildSelectExpressions() method, which uses the ImplicitlyCastResolver to cast a supported type if necessary.

A conversion of column schema is used Instead of just allowing the schema during the validation in the EngineExecutor.validateExistingSink(). The reason is that SchemaRegistry/AVRO does not allow some type of conversions, like INT/BIGINT -> DECIMAL as they are incompatible.

The validation in the EngineExecutor.validateExistingSink()`` is required only for DECIMAL -> DECIMAL of different precision and scale. ImplicitlyCastResolver` can only convert to a different scale, but precision is based on the literal number. Without this, the validation will fail due to a different precision.

Implicitly cast is supported on the following literal types:

• INT,BIGINT,DOUBLE -> DECIMAL
• DECIMAL -> DECIMAL from lower to higher precision/scale

When casting any number to DECIMAL, the ImplicitlyCastResolver makes sure that the precision/scale of the number is compatible with the target decimal precision/scale. The DecimalUtil.canImplicitlyCast() is used to check that.

The reason to not allow non-literals numbers is because INT,BIGINT,DOUBLE numbers found in the topic records might have different precision than the one defined in the target decimal: i.e. DOUBLE -> DECIMAL(1,0).

Other implicitly conversions, such as INT -> BIGINT,DOUBLE, BIGINT -> DOUBLE are not possible yet as there's another refactor to do to support that. Turns out that when the INT -> BIGINT is allowed by this PR, then when the node reads the statement text from the command topic and parses it, it creates an IntegerLiteral instead of the desired LongLiteral. More refactoring is needed to support that, but this PR is fixing only #5285 for now.

Testing done

• Added unit tests

Reviewer checklist

• Ensure docs are updated if necessary. (eg. if a user visible feature is being added or changed).
• Ensure relevant issues are linked (description should include text like "Fixes #")

[stevenpyzhang]

LGTM