Spring Fix SpEL comparison operator for comparable types

This is my first contribution to spring, so please advise if I have missed anything.

This PR fixes SPR-16141 by allowing equality checking to defer to the TypeComparator's canCompare, rather than hardcoding conditions.

Comment From: aclement

Some feedback... I wouldn't create a new test class, just add the test to the existing SpelReproTests. Update the years for files changed and the author tags. For changes made to SpEL behavior these days you need to consider any impact on compiled SpEL. Do the changes to Operator mean changes to the isCompilableXX or generateComparisonCode methods? I can't remember what the compiler does for custom comparators.

Comment From: GleyderC

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