Selector: Inline Sizzle into the selector module

Selector: Inline Sizzle into the selector module

This commit removes Sizzle from jQuery, inlining its code & removing obsolete
workarounds where applicable.

The selector-native module has been removed. Further work on the selector
module may decrease the size enough that it will no longer be necessary. If
it turns out it's still useful, we'll reinstate it but the code will look
different anyway as we'll want to share as much code as possible with
the existing selector module.

The Sizzle AUTHORS.txt file has been merged with the jQuery one - people are
sorted by their first contributions to either of the two repositories.

The commit reduces the gzipped jQuery size by 1460 bytes compared to master.

Closes gh-4395