Remove more dtype canonicalization.

[copybara-service]

Remove more dtype canonicalization.

Notable changes:

• Remove dtype canonicalization from many lax dtype rules. Dtype rules should always talk about post-canonicalized types.
• Use check_and_canonicalize_user_dtype instead of canonicalize_dtype in many user-callable lax functions.
• Change some calls to lax functions to pass canonicalized types to avoid new user warnings.
• Move _convert_and_clip_integer into random.py, which is its only user.
• In passing, rename _input_dtype to input_dtype because it is exported from its enclosing module.