Add Json.newBuilder utility

[cchantep]

Pull Request Checklist

• Have you read through the contributor guidelines?
• Have you squashed your commits?
• Have you added copyright headers to new files?
• Have you updated the documentation?
• Have you added tests for any changed functionality?

Purpose

Add an utility function Json.newBuilder (similar to Map.newBuilder):

import play.api.libs.json.{ Json, JsObject }

// Create a new builder
val builder: JsObjectBuilder = JsObject.newBuilder

// Add key-value pairs to the builder
builder += ("name" -> "John Doe")
builder += ("age" -> 25)

// Clear the builder
builder.clear()

// Add more key-value pairs
builder += ("email" -> "john.doe@example.com")
builder += ("address" -> "123 Street")

// Build the final JsObject
val result: JsObject = builder.result()

// Print the resulting JsObject
println(result)

Will print:

{"email":"john.doe@example.com","address":"123 Street"}

[mkurz]

Looks alright.