Keep json macro by default but allow configuring a list of interpolater names.

It's more readable to have json""" "str" """ rather than json""""str""""

Given the following code:

val inception =
    json"""{"key3": ${ json"""{"key2": "v" }""" } }"""

The formatter outputs:

val inception =
    json"""{
      "key3" : ${json"""{"key2": "v" }"""}
    }"""

The goal is for it to output the something like the following instead:

val inception =
    json"""{
      "key3" : ${json"""{
                   "key2" : "v" 
                 }"""}
    }"""

No need to break json"""{}""" into multiple lines.

Maybe when the end result of the formatting isn't a multi-line string we could do json"1" instead of json"""1""".