We'll be using it for two distinct tasks:
* Core CSS files will keep prefixes. `grunt autoprefixer:core` will update files directly in src/ as a pre-commit step, rather than doing it on build.
* Color CSS files will receive prefixes when they are built.
This commit:
* Adds prefixes we were missing to core CSS.
* Removes prefixes that we no longer need from core CSS.
* Removes all prefixes from colors CSS.
props ocean90.
fixes#27078.
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