Produce nicer style formatting

[mourner]

Makes the format function in the style-spec package produce nicer, more readable style JSON. Before:

"text-size": [
    "interpolate",
    [
        "linear"
    ],
    [
        "zoom"
    ],
    2,
    [
        "step",
        [
            "get",
            "scalerank"
        ],
        13,
        3,
        11,
        5,
        9
    ],
    9,
    [
        "step",
        [
            "get",
            "scalerank"
        ],
        35,
        3,
        27,
        5,
        22
    ]
]

After:

"text-size": [
    "interpolate",
    ["linear"],
    ["zoom"],
    2,
    ["step", ["get", "scalerank"], 13, 3, 11, 5, 9],
    9,
    ["step", ["get", "scalerank"], 35, 3, 27, 5, 22]
]

cc @samanpwbb not sure if this needs any actions on the Studio side. Just wanted to make the downloaded styles in Studio easier to read.

Launch Checklist

• briefly describe the changes in this PR
• write tests for all new functionality (formatting doesn't need to be tested)
• document any changes to public APIs no changes