[perl #34394] [TODO] implement the splice vtable in *PMCArrays

[Leopold Toetsch]

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The splice opcode has the functionality of the perl5 function, so that
should be rather straight to implement. See also classes/array.pmc:splice.

FixedPMCArray can have a splice too, if the array limit isn't hit.

Other <type>*Arrays should first be adapted to the allocation scheme and
layout of the *PMCArray types.

Oh well, while at it, the *BooleanArray should just use one bit per item
not an INTVAL.

leo