Upgrade to TS 4.3 and play nicely with new flags

[dfreeman]

This upgrades the Glint codebase to typescript@4.3 and ensures we play nicely with noImplicitOverride and noPropertyAccessFromIndexSignature.

For noImplicitOverride, we could run afoul when defining a template on a subclass of some other component that already had an associated template. Since we can't know during emit whether or not to use override, for now we include the class name as part of the template key to avoid collisions. Though it's not included in the TS 4.4 Beta blog post, class static blocks look to be landing as part of that release, at which point we can make use of those for template definitions and the need for a field name goes away entirely.

For noPropertyAccessFromIndexSignature, the main culprit I was able to identify where we might trigger that inappropriately was the case of accessing named block params, in particular in the presence of prior type errors, since that could cause 𝛄.blockParams to fall back to the base type with an index signature rather than properly resolving. We now always access block params with [] notation.