Add support for relative ordering

Overview

Our current support for @Order/Ordered uses an absolute number with a default value of "lowest precedence" (i.e. Integer.MAX_VALUE). We also have PriorityOrdered to override such ordering in certain scenarios.

One problem with the current default value is that it is not natural for customizers where you'd want the "default" ones to be at a given order with the ability of custom instance to run before, or after. Such a default must provide a value as there is no way to run "after" with the current default value. A natural value for that is zero with negative values being processed before and positive values being processed after.

A better way to express ordering is to express it relative to another concept. You may need to run/customize/execute before or after another "instance". In Spring Boot, we've essentially implemented that with @AutoConfigureBefore and @AutoConfigureAfter to order auto-configurations.

This issue is to discuss if there is an appetite to provide such constructs in the core framework, with an SPI that would let us order things (potentially being honored in ObjectProvider#orderedStream().

Related Issues

• #34670

Start by reviewing the issue's references to @Order, Ordered, PriorityOrdered, and ObjectProvider#orderedStream(), then compare them with Spring Boot's @AutoConfigureBefore and @AutoConfigureAfter approach. Done would require an agreed core-framework SPI and defined relative-ordering behavior; the issue currently asks whether such a design should exist.