FMMultivalueLink inherits from SequenceableCollection

[Gabriel-Darbord]

Instead of Collection.

Add new: to be compatible with the SequenceableCollection API.
Add setCollection: to make new: work with the intended pre-sizing mechanism.
Remove hash and first to ninth because they are defined in SequenceableCollection.

This might make FMMultivalueLink faster because of the optimized versions of select:thenCollect:&co, although I haven't tried it.

I'm also considering about removing the = method, which only differs from SequenceableCollection's by calling asOrderedCollection on the other collection, but that may be unnecessary (and thus slower for no reason).

	self == otherCollection ifTrue: [^ true].
	self species == otherCollection species ifFalse: [^ false].
	^ values hasEqualElements: otherCollection "=>" asOrderedCollection "<= unnecessary?"

[Gabriel-Darbord]

The tests pass but this doesn't work as expected: we get errors when using basic Collection methods like collect:.

[jecisc]

Do we revert?