Preserve comments with @license or @preserve in TemplatesCompactPrinter.

Allow the TemplatesCompactPrinter (used for compiling CSS for
modulesets) to preserve comments if they have either an @license or
@preserve annotation. The @license annotation will emit the comment,
"END OF LICENSED CSS FILE" at the end of the file.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=106699850

Author: iflan