Use the `Base` type alias from
https://github.com/llvm/llvm-project/pull/158433.

This patch updates the following ops to use `source` (instead of
`vector`) as the name for their source argument:
  * `vector.extract`
  * `vector.scalable.extract`
  * `vector.extract_strided_slice`

This change ensures naming consistency with the "builders" for these Ops
that already use the name `source` rather than `vector`. It also
addresses part of:
  * https://github.com/llvm/llvm-project/issues/131602

Specifically, it ensures that we use `source` and `dest` for read and
write operations, respectively (as opposed to `vector` and `dest`).

This is part of vector.splat deprecation
Reference: https://discourse.llvm.org/t/rfc-mlir-vector-deprecate-then-remove-vector-splat/87143/5
Instead of creating vector::SplatOp, create vector::BroadcastOp

See https://github.com/llvm/llvm-project/pull/147168 for more info.

This change standardises the naming convention for the argument
representing the value to store in various vector operations.
Specifically, it ensures that all vector ops storing a value—whether
into memory, a tensor, or another vector — use `valueToStore` for the
corresponding argument name.

Updated operations:
* `vector.transfer_write`, `vector.insert`, `vector.scalable_insert`,
  `vector.insert_strided_slice`.

For reference, here are operations that currently use `valueToStore`:
* `vector.store` `vector.scatter`, `vector.compressstore`,
  `vector.maskedstore`.

This change is non-functional (NFC) and does not affect the
functionality of these operations.

Implements #131602

It looks like scalable `vector.insertslice/extractslice` ops made their way
through lowering patterns that generate `vector.shuffle` ops. I'm not
sure why this wasn't caught by the verifier, probably because the
shuffle op was folded into something else as part of the same rewrite
and the IR wasn't verified.

This PR fixes the issue by preventing scalable vector.insertslice/extractslice
ops to be lowered to vector shuffles. Instead, they are now lowered to a
sequence of insertslice/extractelement ops using an existing patter.

This patch removes trivial usages of
vector.extractelement/vector.insertelement. These operations can be
fully represented by vector.extract/vector.insert. See
https://discourse.llvm.org/t/rfc-psa-remove-vector-extractelement-and-vector-insertelement-ops-in-favor-of-vector-extract-and-vector-insert-ops/71116
for more information.

Further patches will remove more usages of these ops.

This is a reasonable canonicalization because `extract` is more
constrained than `extract_strided_slices`, so there is no loss of
semantics here, just lifting an op to a special-case higher/constrained
op. And the additional `shape_cast` is merely adding leading unit dims
to match the original result type.

Context: discussion on #111541. I wasn't sure how this would turn out,
but in the process of writing this PR, I discovered at least 2 bugs in
the pattern introduced in #111541, which shows the value of shared
canonicalization patterns which are exercised on a high number of
testcases.

---------

Signed-off-by: Benoit Jacob <jacob.benoit.1@gmail.com>

Co-authored-by: Andrzej Warzyński <andrzej.warzynski@gmail.com>

Co-authored-by: Jakub Kuderski <kubakuderski@gmail.com>