Enable noUncheckedIndexedAccess typescript option

[jkomoros]

Without it, object index accesses are assumed to always succed, which means there are cases where a value could be undefined that Typescript wouldn't report.

noUncheckedIndexedAccess

[jkomoros]

Wow is this a pain in the butt to mechanically add!

When adding it:

Modify tsconfig.json to add noUncheckedIndexedAccess and also nocommit, and then make changes, then if you want to make sure you didn't bfreak anything, stash tsconfig and check it's ok to land then unstash