feat: add decimal argument support to round function

The round function has a number of variants to support different numeric types.  This commit adds support for rounding decimals.

The precision and scale of the resultant decimal type is
calculated from the input decimal parameters and the scale
argument according to the logic in the Spark implementation:
https://github.com/apache/spark/blob/master/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/mathExpressions.scala#L1492

Signed-off-by: Andrew Coleman <[email protected]>

extensions/functions_rounding_decimal.yaml

@@ -0,0 +1,80 @@
+%YAML 1.2
+---
+scalar_functions:
+  -
+    name: "ceil"
+    description: >
+      Rounding to the ceiling of the value `x`.
+    impls:
+      - args:
+          - value: decimal<P,S>
+            name: x
+        return: |-
+          integral_least_num_digits = P - S + 1
+          precision = min(integral_least_num_digits, 38)
+          decimal?<precision, 0>
+  -
+    name: "floor"
+    description: >
+      Rounding to the floor of the value `x`.
+    impls:
+      - args:
+          - value: decimal<P,S>
+            name: x
+        return: |-
+          integral_least_num_digits = P - S + 1
+          precision = min(integral_least_num_digits, 38)
+          decimal?<precision, 0>
+  -
+    name: "round"
+    description: >
+      Rounding the value `x` to `s` decimal places.
+    impls:
+      - args:
+          - value: decimal<P1,S1>
+            name: x
+            description: >
+              Numerical expression to be rounded.
+          - value: i32
+            name: s
+            description: >
+              Number of decimal places to be rounded to.
+
+              When `s` is a positive number, the rounding
+              is performed to a `s` number of decimal places.
+
+              When `s` is a negative number, the rounding is
+              performed to the left side of the decimal point
+              as specified by `s`.
+
+              The precision and scale of the resultant decimal
+              type will be adjusted from the input decimal type
+              dependent on the value of `s`.
+        options:
+          rounding:
+            description: >
+              When a boundary is computed to lie somewhere between two values,
+              and this value cannot be exactly represented, this specifies how
+              to round it.
+
+                - TIE_TO_EVEN: round to nearest value; if exactly halfway, tie
+                  to the even option.
+                - TIE_AWAY_FROM_ZERO: round to nearest value; if exactly
+                  halfway, tie away from zero.
+                - TRUNCATE: always round toward zero.
+                - CEILING: always round toward positive infinity.
+                - FLOOR: always round toward negative infinity.
+                - AWAY_FROM_ZERO: round negative values with FLOOR rule, round positive values with CEILING rule
+                - TIE_DOWN: round ties with FLOOR rule
+                - TIE_UP: round ties with CEILING rule
+                - TIE_TOWARDS_ZERO: round ties with TRUNCATE rule
+                - TIE_TO_ODD: round to nearest value; if exactly halfway, tie
+                  to the odd option.
+            values: [ TIE_TO_EVEN, TIE_AWAY_FROM_ZERO, TRUNCATE, CEILING, FLOOR,
+              AWAY_FROM_ZERO, TIE_DOWN, TIE_UP, TIE_TOWARDS_ZERO, TIE_TO_ODD ]
+        nullability: DECLARED_OUTPUT
+        return: |-
+          integral_digits = P1 - S1 + 1
+          scale = s > 0 ? min(s, S1) : 0
+          precision = s > 0 ? min(integral_digits + scale, 38) : min(max(integral_num_digits, 1- s), 38)
+          decimal?<precision, scale>

tests/cases/rounding_decimal/ceil_decimal.test

@@ -0,0 +1,7 @@
+### SUBSTRAIT_SCALAR_TEST: v1.0
+### SUBSTRAIT_INCLUDE: '/extensions/functions_rounding_decimal.yaml'
+
+# basic: Basic examples without any special cases
+ceil(2.25::dec<8,2>) = 3::dec<7,0>
+ceil(-65.5::dec<8,2>) = -65::dec<7,0>
+ceil(9.9::dec<2,1>) = 10::dec<2,0>

tests/cases/rounding_decimal/floor_decimal.test

@@ -0,0 +1,6 @@
+### SUBSTRAIT_SCALAR_TEST: v1.0
+### SUBSTRAIT_INCLUDE: '/extensions/functions_rounding_decimal.yaml'
+
+# basic: Basic examples without any special cases
+floor(2.25::dec<8,2>) = 2::dec<7,0>
+floor(-65.5::dec<8,2>) = -66::dec<7,0>

tests/cases/rounding_decimal/round_decimal.test

@@ -0,0 +1,11 @@
+### SUBSTRAIT_SCALAR_TEST: v1.0
+### SUBSTRAIT_INCLUDE: '/extensions/functions_rounding_decimal.yaml'
+
+# basic: Basic examples without any special cases
+round(2::dec<2,0>, 2::i32) = 2::dec<3,0>
+round(2.75::dec<8,2>, 1::i32) = 2.8::dec<8,1>
+
+# negative_rounding: Examples with negative rounding
+round(2::dec<2,0>, -2::i32) = 0::dec<2,0>
+round(123::dec<2,0>, -2::i32) = 100::dec<2,0>
+round(8793::dec<2,0>, -2::i32) = 8800::dec<2,0>