[mlir][sparse] simplify some header code (#70989)

This is a first revision in a small series of changes that removes
duplications between direct encoding methods and sparse tensor type
wrapper methods (in favor of the latter abstraction, since it provides
more safety). The goal is to simply end up with "just" SparseTensorType

mlir/lib/Dialect/SparseTensor/Transforms/SparseTensorCodegen.cpp

@@ -178,7 +178,7 @@ static void createAllocFields(OpBuilder &builder, Location loc,
   SmallVector<Value> dimSizes;
   dimSizes.reserve(dimRank);
   unsigned i = 0; // cumulative index into `dynSizes`.
-  for (const DynSize sh : stt.getDimShape())
+  for (const Size sh : stt.getDimShape())
     dimSizes.push_back(ShapedType::isDynamic(sh)
                            ? dynSizes[i++]
                            : constantIndex(builder, loc, sh));