Move publish target to es2020

[Pessimistress]

See #9183

Input:

export default class Deck {
   static defaultProps = defaultProps;
   static VERSION = VERSION; 
}

Output targeting ES2022:

export default class Deck {
    static { this.defaultProps = defaultProps; }
    static { this.VERSION = VERSION; }
}

Output targeting ES2020:

class Deck {
}
Deck.defaultProps = defaultProps;
Deck.VERSION = VERSION;
export default Deck;

[coveralls]

coverage: 91.733%. remained the same
when pulling 4178b33 on x/target
into 0b8fdd8 on master.

[ibgreen]

LGTM.

Interestingly, the TypeScript target docs only talk about "downleveling" seems we had a case of "upleveling" happening here: https://www.typescriptlang.org/tsconfig/#target