ESQL: Introduce a casting operator, :: (elastic#107409)

This adds support for an "inline" casting operator, `::`. The operator
can be used with literals, fields and functions.

The operator delegates to one the existing `to_xxx()` conversion
functions, so only the types for which such a converter exist can be
cast to with the new opeator.

For convenience, a list of type name aliases are introduced as well.

Example: `ROW 1::bool, "1"::int`

docs/changelog/107409.yaml

@@ -0,0 +1,5 @@
+pr: 107409
+summary: "ESQL: Introduce a casting operator, `::`"
+area: ES|QL
+type: feature
+issues: []

x-pack/plugin/esql/qa/testFixtures/src/main/resources/convert.csv-spec

@@ -0,0 +1,169 @@
+// Conversion-specific tests
+
+convertToBoolean
+required_feature: esql.casting_operator
+ROW zero=0::boolean, one=1::bool
+;
+
+ zero:boolean  | one:boolean
+false          |true
+;
+
+convertToInteger
+required_feature: esql.casting_operator
+ROW zero="0"::integer, one="1"::int
+;
+
+ zero:integer  | one:integer
+0              |1
+;
+
+convertToIP
+required_feature: esql.casting_operator
+ROW ip="1.1.1.1"::ip
+;
+
+ ip:ip       
+1.1.1.1        
+;
+
+convertToLong
+required_feature: esql.casting_operator
+ROW long="-1"::long
+;
+
+long:long
+-1
+;
+
+convertToLongWithWarning
+required_feature: esql.casting_operator
+ROW long="1.1.1.1"::long
+;
+warning:Line 1:10: evaluation of [\"1.1.1.1\"::long] failed, treating result as null. Only first 20 failures recorded.
+warning:Line 1:10: org.elasticsearch.xpack.ql.InvalidArgumentException: Cannot parse number [1.1.1.1]
+
+long:long
+null
+;
+
+convertToDouble
+required_feature: esql.casting_operator
+ROW zero="0"::double
+;
+
+ zero:double
+0.0
+;
+
+convertToString
+required_feature: esql.casting_operator
+ROW one=1::keyword, two=2::text, three=3::string
+;
+
+ one:keyword   | two:keyword   | three:keyword
+1              |2              |3
+;
+
+convertToDatetime
+required_feature: esql.casting_operator
+ROW date="1985-01-01T00:00:00Z"::datetime, zero=0::datetime
+;
+
+ date:datetime          | zero:datetime
+1985-01-01T00:00:00.000Z|1970-01-01T00:00:00.000Z
+;
+
+convertToVersion
+required_feature: esql.casting_operator
+ROW ver="1.2.3"::version
+;
+
+ ver:version
+1.2.3
+;
+
+convertToUnsignedLong
+required_feature: esql.casting_operator
+ROW zero="0"::unsigned_long, two=abs(-2)::UnsigneD_LOng
+;
+
+ zero:unsigned_long | two:unsigned_long
+0                   |2
+;
+
+convertToGeoPoint
+required_feature: esql.casting_operator
+ROW gp="POINT(0 0)"::geo_point
+;
+
+ gp:geo_point
+POINT (0.0 0.0)
+;
+
+convertToGeoShape
+required_feature: esql.casting_operator
+ROW gs="POINT(0 0)"::geo_shape
+;
+
+ gs:geo_shape
+POINT (0.0 0.0)
+;
+
+convertToCartesianPoint
+required_feature: esql.casting_operator
+ROW cp="POINT(0 0)"::cartesian_point
+;
+
+ cp:cartesian_point
+POINT (0.0 0.0)
+;
+
+convertToCartesianShape
+required_feature: esql.casting_operator
+ROW cs="POINT(0 0)"::cartesian_shape
+;
+
+ cs:cartesian_shape
+POINT (0.0 0.0)
+;
+
+convertChained
+required_feature: esql.casting_operator
+ROW one=1::STRING::LONG::BOOL
+;
+
+one:boolean
+true
+;
+
+convertWithIndexMultipleConversionsInSameExpressionAndConversionInFiltering
+required_feature: esql.casting_operator
+ FROM employees
+| EVAL en_str=emp_no::STRING, bd=ABS(birth_date::LONG)::STRING
+| KEEP en_str, emp_no, bd, birth_date
+| WHERE ABS(birth_date::LONG) < 176169600000
+| SORT emp_no
+;
+
+ en_str:keyword| emp_no:integer| bd:keyword    | birth_date:datetime       
+10092          |10092          |164246400000   |1964-10-18T00:00:00.000Z
+10093          |10093          |175392000000   |1964-06-11T00:00:00.000Z
+10095          |10095          |157593600000   |1965-01-03T00:00:00.000Z
+;
+
+convertWithBoolExpressionAndQualifiedName
+required_feature: esql.casting_operator
+ FROM employees
+| EVAL neg = (NOT still_hired)::string, sf = ROUND(height.scaled_float::double, 2)
+| KEEP emp_no, still_hired, neg, sf
+| SORT emp_no
+| WHERE neg == "false"
+| LIMIT 3
+;
+
+ emp_no:integer| still_hired:boolean | neg:keyword   | sf:double
+10001          |true                 |false          |2.03
+10002          |true                 |false          |2.08
+10004          |true                 |false          |1.78
+;

x-pack/plugin/esql/src/main/antlr/EsqlBaseLexer.g4

@@ -110,6 +110,7 @@ BY : 'by';
 AND : 'and';
 ASC : 'asc';
 ASSIGN : '=';
+CAST_OP : '::';
 COMMA : ',';
 DESC : 'desc';
 DOT : '.';