Implement v_magnitude function (elastic#132765)

Implements v_magnitude ESQL function

Author: svilen-mihaylov-elastic

docs/changelog/132765.yaml

@@ -0,0 +1,5 @@
+pr: 132765
+summary: Implement `v_magnitude` function
+area: ES|QL
+type: feature
+issues: [132768]

docs/reference/query-languages/esql/_snippets/functions/description/v_magnitude.md

@@ -0,0 +1,87 @@
+ # Tests for v_magnitude scalar function
+ 
+ magnitudeWithVectorField
+ required_capability: magnitude_scalar_vector_function
+ 
+// tag::vector-magnitude[]
+ from colors
+ | eval magnitude = v_magnitude(rgb_vector) 
+ | sort magnitude desc, color asc 
+// end::vector-magnitude[]
+ | limit 10
+ | keep color, magnitude
+ ;
+ 
+// tag::vector-magnitude-result[]
+color:text | magnitude:double
+white      | 441.6729431152344
+snow       | 435.9185791015625
+azure      | 433.1858825683594
+ivory      | 433.1858825683594
+mint cream | 433.0704345703125
+sea shell  | 426.25579833984375
+honeydew   | 424.5291442871094
+old lace   | 420.6352233886719
+corn silk  | 418.2451477050781
+linen      | 415.93267822265625
+// end::vector-magnitude-result[] 
+;
+
+ magnitudeAsPartOfExpression
+ required_capability: magnitude_scalar_vector_function
+ 
+ from colors
+ | eval score = round((1 + v_magnitude(rgb_vector) / 2), 3) 
+ | sort score desc, color asc 
+ | limit 10
+ | keep color, score
+ ;
+
+color:text | score:double
+white      | 221.836
+snow       | 218.959
+azure      | 217.593
+ivory      | 217.593
+mint cream | 217.535
+sea shell  | 214.128
+honeydew   | 213.265
+old lace   | 211.318
+corn silk  | 210.123
+linen      | 208.966
+;
+
+magnitudeWithLiteralVectors
+required_capability: magnitude_scalar_vector_function
+ 
+row a = 1
+| eval magnitude = round(v_magnitude([1, 2, 3]), 3) 
+| keep magnitude
+;
+
+magnitude:double
+3.742
+;
+
+ magnitudeWithStats
+ required_capability: magnitude_scalar_vector_function
+ 
+ from colors
+ | eval magnitude = round(v_magnitude(rgb_vector), 3) 
+ | stats avg = round(avg(magnitude), 3), min = min(magnitude), max = max(magnitude)
+ ;
+
+avg:double | min:double | max:double
+313.692    | 0.0        | 441.673
+;
+
+magnitudeWithNull
+required_capability: magnitude_scalar_vector_function
+
+row a = 1
+| eval magnitude = v_magnitude(null) 
+| keep magnitude
+;
+
+magnitude:double
+null
+;

docs/reference/query-languages/esql/_snippets/functions/examples/v_magnitude.md

@@ -1356,6 +1356,11 @@ public enum Cap {
          */
         CORRECT_SKIPPED_SHARDS_COUNT,
 
+        /*
+         * Support for calculating the scalar vector magnitude.
+         */
+        MAGNITUDE_SCALAR_VECTOR_FUNCTION(Build.current().isSnapshot()),
+
         /**
          * Byte elements dense vector field type support.
          */