[3.0.0] Various product GQL fixes

[aldeed]

Resolves #6034
Resolves #6044
Impact: minor
Type: bugfix

Fixes

• Refactored createProduct, createProductVariant, updateProduct, and updateProductVariant mutations, fixing and optimizing various things
• The arguments to "afterVariantUpdate" event were not being consistently emitted and used. Now they are. Also, it's now called once with fields rather than many times with field.
• Removed unneeded stuff (label, defaultValue, etc.) from product and variant SimpleSchemas
• Fix GQL/input schemas for updateProduct and updateProductVariant so that you can't update things like _id and ancestors that would cause errors or be insecure.
• Fix handling of email addresses when inviting emails that don't already have an account. The case in which an admin enters the invite email no longer has to match the case in which the invitee enters it when registering. [3.0.0] AccountInvites are case-sensitive #6034
• Update products GQL query to have a default sort of createdAt descending. Ensure that we're always setting createdAt and updatedAt properly everywhere. Add default sort for products API as createdAt ascending #6044

Breaking changes

The refactor of the "afterVariantUpdate" emits is technically breaking, but it was previously broken, so now it's double broken, which equals fixed.

Testing

• Review code of the refactored mutations and test them
• Test inviting with different email case (see steps in [3.0.0] AccountInvites are case-sensitive #6034)
• Test various sortOrder and sortBy params for products GQL query

[mikemurray]

👍