Restore full representation of rejected value in FieldError.toString()

We would preferably use ObjectUtils.nullSafeConciseToString(rejectedValue) here but revert to the full nullSafeToString representation for strict backwards compatibility (programmatic toString calls as well as exception messages).

Closes gh-30799

(cherry picked from commit 1dc9dff)

spring-context/src/main/java/org/springframework/validation/FieldError.java

@@ -124,8 +124,10 @@ public int hashCode() {
 
 	@Override
 	public String toString() {
+		// We would preferably use ObjectUtils.nullSafeConciseToString(rejectedValue) here but
+		// keep including the full nullSafeToString representation for backwards compatibility.
 		return "Field error in object '" + getObjectName() + "' on field '" + this.field +
-				"': rejected value [" + ObjectUtils.nullSafeConciseToString(this.rejectedValue) + "]; " +
+				"': rejected value [" + ObjectUtils.nullSafeToString(this.rejectedValue) + "]; " +
 				resolvableToString();
 	}