Trim blank lines from generated renderers

[srawlins]

Not a big deal, but this trims newlines both from the checked in AOT template renderers (~500 newlines), and also from the rendered HTML output. I wanted to play with the idea and found the impl so simple that it seems like an easy win.

Fewer blank lines in the rendered HTML make it easier to scroll through in a failed unit test, or a log, or on disk. A single removed line in a generated AOT template renderer could be something that is executed in a loop, representing n removed newlines in the rendered HTML. (It's also fewer bytes but I would be surprised if that was anything but negligible.)

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[srawlins]

CC @dart-lang/analyzer-team