Core: render Swift AST sections properly when dumping

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trafficstars

Adjust the rendering for the Swift AST section when listing the sections to make it easy to identify when scanning. We already have a diff to break in the switch, might as well as take the opportunity to render the string.

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CC: @bulbazord @JDevlieghere @kastiglione

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@swift-ci please test

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@swift-ci please test Windows platform