Better align TypeScript type checking in web-forms, .vue modules

[eyelidlessness]

As I've been reviewing #183, trying a change I want to suggest produced a very surprising type for a destructured array member. What surprised me is that I expected it to be string | undefined, but it is not!

As it turns out, the TypeScript configurations in @getodk/web-forms are much less strict than throughout the rest of the project. We should make these consistent. We should also consider sharing a great deal more between configs so it's less likely for discrepancies like this to occur.

[eyelidlessness]

We probably want to align more, but these definitely stand out:

• strict should be true
• noUncheckedIndexedAccess, which is oddly not part of the strict catch-all, should also be true