[mlir][Vector] Add constant folding for vector.from_elements operation (#145849)
### Summary
This PR adds a new folding pattern for **vector.from_elements** that
canonicalizes it to **arith.constant** when all input operands are
constants.
### Implementation Details
**Leverages FoldAdaptor capabilities**: Uses adaptor.getElements() to
access **pre-computed** constant attributes, avoiding redundant pattern
matching on operands.
### Example Transformation
```
Before:
%c0_i32 = arith.constant 0 : i32
%c1_i32 = arith.constant 1 : i32
%c2_i32 = arith.constant 2 : i32
%c3_i32 = arith.constant 3 : i32
%v = vector.from_elements %c0_i32, %c1_i32, %c2_i32, %c3_i32 : vector<2x2xi32>
After:
%v = arith.constant dense<[[0, 1], [2, 3]]> : vector<2x2xi32>
```
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Co-authored-by: Yang Bai <yangb@nvidia.com>
393a75ebb7