[enhance] Small bundle reduction by using typescript 'declare'

[ntucker]

Motivation

TypeScript 3.7 introduced a new 'declare' property modifier, which enables declaring property types without setting the default to void 0 in javascript. This is useful when they are actually set in the constructor. The end result is several lines removed from output that don't need to be executed.

Solution

We also start using optional chaining in tests. We need the latest prettier to work with this new syntax.

Optional chaining is not used in the main code as it results in extra output bloat.

Before

src/index.ts → dist/index.umd.min.js...
┌────────────────────────────────────────┐
│ │
│ Destination: dist/index.umd.min.js │
│ Bundle Size: 21.53 KB │
│ Minified Size: 21.43 KB │
│ Gzipped Size: 6.86 KB │
│ │
└────────────────────────────────────────┘

After

src/index.ts → dist/index.umd.min.js...
┌────────────────────────────────────────┐
│ │
│ Destination: dist/index.umd.min.js │
│ Bundle Size: 21 KB │
│ Minified Size: 20.9 KB │
│ Gzipped Size: 6.76 KB │
│ │
└────────────────────────────────────────┘