internal/mcp: unify json tag parsing

Do a thorough job of parsing json struct tags.

Move the code to a place where both mcp and jsonschema can use it.

Change-Id: I6c86308834706b12a1e22cd96ae120590f49d3f4
Reviewed-on: https://go-review.googlesource.com/c/tools/+/678757
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Findley <rfindley@google.com>

jsonschema/schema.go

@@ -17,6 +17,8 @@ import (
 	"reflect"
 	"regexp"
 	"slices"
+
+	"github.com/modelcontextprotocol/go-sdk/internal/util"
 )
 
 // A Schema is a JSON schema object.
@@ -426,8 +428,9 @@ var (
 
 func init() {
 	for _, sf := range reflect.VisibleFields(reflect.TypeFor[Schema]()) {
-		if name, ok := jsonName(sf); ok {
-			schemaFieldInfos = append(schemaFieldInfos, structFieldInfo{sf, name})
+		info := util.FieldJSONInfo(sf)
+		if !info.Omit {
+			schemaFieldInfos = append(schemaFieldInfos, structFieldInfo{sf, info.Name})
 		}
 	}
 	slices.SortFunc(schemaFieldInfos, func(i1, i2 structFieldInfo) int {