datetime: check overflow after interval operations

We may overflow supported years range if we proceed
(multiple times) interval addition or subtraction operations.
At the end of add/sub we check all interval subcomponents
on validity of their value. Result of this check is returned
in the encoded value to the Lua side, where less than 0 means
underflow in some component, and greater than 0 overflow in
subcomponent.

Part of #6923

NO_DOC=fix
NO_CHANGELOG=fix