Switch core packages to stricter types

[JasonVMo]

Platforms Impacted

• all / none

Description of changes

This moves several core packages to the strict tsconfigs. This adds:

• stronger types, particularly around object and style merging
• default values for checked state which shouldn't change behavior unless there was a bug as it makes the pre-initialized state consistent with the unchecked state. Previously it would go undefined -> true -> false, now it alternates between true and false.
• this reapplies the changes from: PR 4058