CMakeLists: Make most implicit type conversion warnings errors on MSVC

Quite frequently there have been cases where code has been merged into
the core that produces warning. In order to prevent this from occurring,
we can make the compiler flag these cases and allow our CI to flag down
any code that would generate these warnings.

This is beneficial given silent conversions from signed/unsigned can
result in logic bugs. This forces one writing changes to be explicit
about when signedness conversions are desirable, rather than leaving it
up to readers' interpretation.

Currently the codebase isn't in a state where it will build successfully
with this change applied, but this will be addressed in subsequent
follow-up changes. This set of changes will focus on making it build
properly with these changes for MSVC as a starting point for basic
coverage.