sage.structure.mutability: Add global is_mutable, is_immutable functions

[mkoeppe]

It would

• try ._is_immutable first,
• do an isinstance check against MutableSequence, mutableMapping, MutableSet (https://docs.python.org/3/library/collections.abc.html)
• try .is_immutable()

We could also add an is_immutable() method to Element, making them immutable by default, and perhaps also to UniqueRepresentation, making unique parents immutable.

Related: #15264, #15266, #32496 comment:6

CC: @tscrim @mjungmath

Component: misc

Issue created by migration from https://trac.sagemath.org/ticket/30387

[mkoeppe]

comment:2

Setting new milestone based on a cursory review of ticket status, priority, and last modification date.