Add a lowering for Linalg matmul to LLVM

This CL adds a lowering to LLVM for MamulOp and a corresponding integration test.

View descriptor manipulation is moved from MLIR's LLVM dialect to C++ code compiled on the side. To this end a separation is introduced between `cblas.cpp` and `cblas_interface.cpp`, the latter operating on view types whose ABI correspond to the LLVM signature generated by MLIR.

An intermediary step is introduced that allocates a new descriptor on the MLIR side for the purpose of passing it to LLVM. The reason for this extra step is that the ABI for by-value ViewType objects wants aligned descriptors, e.g.:
```
extern "C" void linalg_dot_impl(ViewType<float, 1> X, ViewType<float, 1> Y,
                                BaseViewType<float> Z) {
   ...
}
```
produces LLVM IR with the signature:
```
%struct.ViewType = type { %struct.BaseViewType, [1 x i64], [1 x i64] }
%struct.BaseViewType = type { float*, i64 }

define void @linalg_dot_impl(%struct.ViewType* byval align 8, %struct.ViewType* byval align 8, float*, i64) tensorflow/mlir#0 {
...
}
```

We don't seem to be able to make such aligned  allocations in the MLIR -> LLVM converter atm.
Going through a level of indirection allows the test to pass.
The temporary tradeoff is that the MLIR shims have to be written by hand.
They will disappear in the future.

PiperOrigin-RevId: 252670672