feat(mysql): Support json.RawMessage for LOAD DATA INFILE (sqlc-dev#3099)

Author: Jille

internal/codegen/golang/templates/go-sql-driver-mysql/copyfromCopy.tmpl

@@ -10,7 +10,7 @@ func convertRowsFor{{.MethodName}}(w *io.PipeWriter, {{.Arg.SlicePair}}) {
 {{- range $arg.CopyFromMySQLFields}}
 {{- if eq .Type "string"}}
 	e.AppendString({{if eq (len $arg.CopyFromMySQLFields) 1}}row{{else}}row.{{.Name}}{{end}})
-{{- else if eq .Type "[]byte"}}
+{{- else if or (eq .Type "[]byte") (eq .Type "json.RawMessage")}}
 	e.AppendBytes({{if eq (len $arg.CopyFromMySQLFields) 1}}row{{else}}row.{{.Name}}{{end}})
 {{- else}}
 	e.AppendValue({{if eq (len $arg.CopyFromMySQLFields) 1}}row{{else}}row.{{.Name}}{{end}})

internal/endtoend/testdata/json/mysql/go/copyfrom.go

@@ -1,2 +1,5 @@
 -- name: SelectFoo :exec
 SELECT * FROM foo;
+
+-- name: BulkInsert :copyfrom
+INSERT INTO foo (a, b) VALUES (?, ?);

internal/endtoend/testdata/json/mysql/go/query.sql.go

@@ -4,6 +4,7 @@
     {
       "path": "go",
       "engine": "mysql",
+      "sql_driver": "github.com/go-sql-driver/mysql",
       "name": "querytest",
       "schema": "schema.sql",
       "queries": "query.sql"