Add a way to pass 2d options to DOM.context2d like willReadFrequently

[bennyschudel]

Hi

Can we add a way here to pass options to getContext('2d'). It seems to me that willReadFrequently is only possible when getting the context for the first time.

https://github.com/observablehq/stdlib/blob/493bf210f5fcd9360cf87a961403aa963ba08c96/src/dom/context2d.js#L7

Best Benny

[mootari]

Fwiw, there's a pending PR: #273