[mlir][Vector] Add a rewrite pattern for gather over a strided memref (#72991)

This patch adds a rewrite pattern for `vector.gather` over a strided
memref like the following:

```mlir
%subview = memref.subview %arg0[0, 0] [100, 1] [1, 1] :
    memref<100x3xf32> to memref<100xf32, strided<[3]>>
%gather = vector.gather %subview[%c0] [%idxs], %cst_0, %cst :
    memref<100xf32, strided<[3]>>, vector<4xindex>, vector<4xi1>, vector<4xf32>
    into vector<4xf32>
```

After the pattern added in this patch:
```mlir
%collapse_shape = memref.collapse_shape %arg0 [[0, 1]] :
    memref<100x3xf32> into memref<300xf32>
%1 = arith.muli %arg3, %cst : vector<4xindex>
%gather = vector.gather %collapse_shape[%c0] [%1], %cst_1, %cst_0 :
    memref<300xf32>, vector<4xindex>, vector<4xi1>, vector<4xf32>
    into vector<4xf32>
```

Fixes https://github.com/openxla/iree/issues/15364.