Manifests should be prettified for easier readability

[jvgaultney]

fontmanifest.json files are intended to be read both by humans as well as scripts, so it should be prettified to match the discussed style, as in this example:

{"lisubosa": {
    "files": {
        "LisuBosa-Regular.ttf": {"axes": {"wght": 400, "ital": 0}},
        "web/LisuBosa-Regular.woff": {"axes": {"wght": 400, "ital": 0}},
        "web/LisuBosa-Regular.woff2": {"axes": {"wght": 400.0, "ital": 0}},
        "LisuBosa-Bold.ttf": {"axes": {"wght": 700, "ital": 0}},
        "web/LisuBosa-Bold.woff": {"axes": {"wght": 700.0, "ital": 0}},
        "web/LisuBosa-Bold.woff2": {"axes": {"wght": 700.0, "ital": 0}},
        "LisuBosa-ExtraBold.ttf": {"axes": {"wght": 800, "ital": 0}, "altfamily": "Lisu Bosa Extra Bold"},
        "web/LisuBosa-ExtraBold.woff": {"axes": {"wght": 800.0, "ital": 0}, "altfamily": "Lisu Bosa Extra Bold"},
        "web/LisuBosa-ExtraBold.woff2": {"axes": {"wght": 800.0, "ital": 0}, "altfamily": "Lisu Bosa Extra Bold"},
        "LisuBosa-Italic.ttf": {"axes": {"wght": 400.0, "ital": 1}},
        "web/LisuBosa-Italic.woff": {"axes": {"wght": 400.0, "ital": 1}},
        "web/LisuBosa-Italic.woff2": {"axes": {"wght": 400.0, "ital": 1}},
        "LisuBosa-BoldItalic.ttf": {"axes": {"wght": 700.0, "ital": 1}},
        "web/LisuBosa-BoldItalic.woff": {"axes": {"wght": 700.0, "ital": 1}},
        "web/LisuBosa-BoldItalic.woff2": {"axes": {"wght": 700.0, "ital": 1}},
        "LisuBosa-ExtraBoldItalic.ttf": {"axes": {"wght": 800.0, "ital": 1}, "altfamily": "Lisu Bosa Extra Bold"},
        "web/LisuBosa-ExtraBoldItalic.woff": {"axes": {"wght": 800.0, "ital": 1}, "altfamily": "Lisu Bosa Extra Bold"},
        "web/LisuBosa-ExtraBoldItalic.woff2": {"axes": {"wght": 800.0, "ital": 1}, "altfamily": "Lisu Bosa Extra Bold"}
        },
    "defaults": {
        "ttf": "LisuBosa-Regular.ttf",
        "woff": "LisuBosa-Regular.woff",
        "woff2": "LisuBosa-Regular.woff2",
        },
    "family": "Lisu Bosa", 
    "version": "6.101"
    }
}