Drop makePositionAttr and the like in favor of Builder::getI64ArrayAttr

The helper functions makePositionAttr() and positionAttr() were originally
introduced in the lowering-to-LLVM-dialect pass to construct integer array
attributes that are used for static positions in extract/insertelement.
Constructing an integer array attribute being fairly common, a utility function
Builder::getI64ArrayAttr was later introduced into the Builder API.  Drop
makePositionAttr and similar homegrown functions and use that API instead.
PiperOrigin-RevId: 269295836