TypeScript strict null checks

[enisdenjo]

strictNullChecks are disabled by default. Meaning, we didn't have checks like "object is possible undefined" which are of outmost importance.

Mesh has many misuses where cases like these are passing:

function accessProp(obj: { prop: string } | undefined) {
  obj.prop; // ✅
}

or

type Obj = { prop: string };
const obj: Obj = { prop: undefined }; // ✅