Remove schema default options in favor of determining schema default options in `Model.compile()`

#7103 exposed an important flaw with how we handle options. The `_userProvidedOptions` construct we use for determining whether a user explicitly set an option or whether we're using a default doesn't work if the user modifies options using `schema.options.optionName = optionValue`. This makes it super messy to handle global options like `strict` in schemas. The problem comes down to the fact that handling global options is hard because schemas set default options in the constructor, so consumers of the schema have no good way to tell whether the user explicitly set an option or the schema constructor used a default.

To work around #7103, we'll tie schemas to globals in a limited way, but up until recently the Mongoose global and the `Schema` constructor have been 100% isolated from each other. I'm wary this may have some unforeseen consequences. In the future, I think we should go back to separating schemas from the Mongoose global.

Start by reading issue #7103 and tracing how schema constructor defaults, `_userProvidedOptions`, `schema.options`, and `Model.compile()` currently interact. The issue is complete when schema defaults are no longer indistinguishable from explicit user options and global options such as `strict` behave correctly without reintroducing the schema-global coupling concerns described here.

Written by the indexing model from the issue text.