[mlir][Linalg] Extend fusion to support WAW atm on buffers.

Summary:
The RAW fusion happens only if the produecer block dominates the consumer block.
The WAW pattern also works with the precondition. I.e., if a producer can
dominate the consumer, they can fairly fuse together.

Since they are all tilable, we can think the pattern like this way:

Input:
```
linalg_op1 view

tile_loop
  subview_2
  linalg_op2 subview_2
```

Tile the first Linalg op as same as the second Linalg.
```
tile_loop
  subview_1
  linalg_op1 subview_1

tile_loop
  subview_2
  liangl_op2 subview_2
```

Since the first Linalg op is tilable in the same way and the computation are
independently, it's fair to fuse it with the second Linalg op.
```
tile_loop
  subview_1
  linalg_op1 subview_1
  linalg_op2 subview_2
```

In short, this patch includes:
- Handling both RAW and WAW pattern.
- Adding a interface method to get input and output buffers.
- Exposing a method to get a StringRef of a dependency type.
- Fixing existing WAW tests and add one more use case: initialize the buffer
  before conv op.

Differential Revision: https://reviews.llvm.org/D76897