fun createChildWithNewPrefix(newPrefix: String): AssertionFormatterMethodObject
Creates an AssertionFormatterMethodObject for kind of a child of the current method object using the given newPrefix (the child will typically be used to indent IAssertions one level more).
Technically speaking it means that the child's indentLevel is based on the current method object but increased by the current method object's prefix.length.
newPrefix - The new prefix to be used.
Return
The newly created AssertionFormatterMethodObject.