Use dot-shorthand syntax for doubles when possible

[elliette]

If a user has a double property that could support dot shorthand syntax but isn't, e.g.:

• double.infinity -> .infinity
• double.nan -> .nan

We could display the dot-shorthand version to help users discover this new language feature. This would require the analysis server to send the current Dart version to the Property Editor Client so that the Property Editor Client can determine whether dot-shorthand syntax is supported.