Add noUncheckedIndexedAccess to tsconfig

[mattrunyon]

microsoft/TypeScript#13778

The issue above explains in detail, but basically without this rule enabled, TypeScript does not complain when a value is possibly undefined because it is accessed via indexing such as myArr[i] or myObj[someStrVar]

We should enable this to better catch any potential errors caused by uncaught undefined values

[mattrunyon]

This rule actually might be more hassle than it's worth. It also adds index checks inside for loops which could get quite annoying. Enabling the rule introduces 167 errors (there are multiple errors fixed by a single check, but still annoying)