Adds the ABS function which returns the absolute (positive) value of a numeric expression.

Changes

• ExpressionFunctions.cs — six overloads covering all supported numeric types: int, bigint, decimal, float, money, real
• FunctionMetadata.cs — autocomplete/IntelliSense entry
• ExpressionFunctionTests.cs — unit tests for int, bigint, and float overloads covering positive, negative, zero, and null inputs

Usage

SELECT ABS(-42)         -- 42
SELECT ABS(-3.14)       -- 3.14
SELECT ABS(amount)      -- works on any numeric column