[Triton-MLIR] Replace triton.extract_slice with tensor.extract_slice and support more general tensor slicing (#837)

## Features

- Allow taking a block of tensor slice, as long as each dimension is
contiguous (unit stride).
- Fix some problems in `insert_slice_async`'s semantic.
- More general verification for ops that return shared layout encoding.

## Known Limitations

- `insert_slice_async` still uses the old semantic. May submit another
PR later to support similar semantic like `tensor.extract_slice`.
- No encoding verification for `tensor.extract_slice`.
- 3d tensor ops are broken.
- Strided accesses are not allowed.
- May cause a little performance slowdown since we are passing strides
as values but not constants (e.g., int).
It would be difficult to pass strides as attributes when we have control
flows. A block argument is possible to accept tensors with different
strides.

lib/Dialect/TritonGPU/IR/Traits.cpp

@@ -0,0 +1,14 @@
+#include "triton/Dialect/TritonGPU/IR/Traits.h"
+#include "triton/Analysis/Utility.h"
+
+mlir::LogicalResult
+mlir::OpTrait::impl::verifyResultsAreSharedEncoding(Operation *op) {
+  if (failed(verifyAtLeastNResults(op, 1)))
+    return failure();
+
+  for (auto result : op->getResults())
+    if (!isSharedEncoding(result))
+      return op->emitOpError() << "requires all results to be shared encoding";
+
+  return success();
+};