Support private properties syntax

[lloydjatkinson]

Feature suggestion

Support private properties: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes/Private_properties

Example:

class Class {
    #example: i32;
}

[mattjohnsonpint]

Is this just a request to support the # syntax instead of private? Or would you expect a difference in functionality?

Considering the feature overview from the TypeScript 3.8 release notes (when it was added), in TypeScript private is "soft privacy" where # is "hard privacy". But in AssemblyScript, since there's no JS transpile, then I believe private is already "hard privacy".