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

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.

A number of places in our codebase special case to use
extractelement/insertelement for 0D vectors, because extract/insert did
not support 0D vectors previously. Since insert/extract support 0D
vectors now, use them instead of special casing.

This PR continues with the introduction of poison as initialization
vector, in this particular case, in LowerVectorBitCast,
LowerVectorBroadcast and LowerVectorTranspose.

Adds tests with scalable vectors for the Vector-To-LLVM conversion pass.
Covers the following Ops:
  * vector.bitcast
  * vector.broadcast

Note, this has uncovered some missing logic in `BroadcastOpLowering`.
This PR fixes the most basic cases where the scalable flags were dropped
and the generated code was incorrect. Also, the conditions in
`vector::isBroadcastableTo` are relaxed to allow cases like this:
```mlir
%0 = vector.broadcast %arg0 : vector<1xf32> to vector<[4]xf32>
```

The `BroadcastOpLowering` pattern is effectively disabled for scalable
vectors in more complex cases where an SCF loop would be required to
loop over the scalable dims, e.g.:
```mlir
 %0 = vector.broadcast %arg0 : vector<[4]x1x2xf32> to vector<[4]x3x2xf32>
```

These cases are marked as "Stretch not at start" in the code. In those
cases, support for scalable vectors is left as a TODO.

This patch is part of a project to move the Presburger library into
LLVM.

This patch makes sure that the following case is lowered correctly
("duplication"):
```
  func.func @broadcast_scalable_duplication(%arg0: vector<[32]xf32>) -> vector<1x[32]xf32> {
    %res = vector.broadcast %arg0 : vector<[32]xf32> to vector<1x[32]xf32>
    return %res : vector<1x[32]xf32>
  }
```

The MLIR classes Type/Attribute/Operation/Op/Value support
cast/dyn_cast/isa/dyn_cast_or_null functionality through llvm's doCast
functionality in addition to defining methods with the same name.
This change begins the migration of uses of the method to the
corresponding function call as has been decided as more consistent.

Note that there still exist classes that only define methods directly,
such as AffineExpr, and this does not include work currently to support
a functional cast/isa call.

Caveats include:
- This clang-tidy script probably has more problems.
- This only touches C++ code, so nothing that is being generated.

Context:
- https://mlir.llvm.org/deprecation/ at "Use the free function variants
  for dyn_cast/cast/isa/…"
- Original discussion at https://discourse.llvm.org/t/preferred-casting-style-going-forward/68443

Implementation:
This first patch was created with the following steps. The intention is
to only do automated changes at first, so I waste less time if it's
reverted, and so the first mass change is more clear as an example to
other teams that will need to follow similar steps.

Steps are described per line, as comments are removed by git:
0. Retrieve the change from the following to build clang-tidy with an
   additional check:
   https://github.com/llvm/llvm-project/compare/main...tpopp:llvm-project:tidy-cast-check
1. Build clang-tidy
2. Run clang-tidy over your entire codebase while disabling all checks
   and enabling the one relevant one. Run on all header files also.
3. Delete .inc files that were also modified, so the next build rebuilds
   them to a pure state.
4. Some changes have been deleted for the following reasons:
   - Some files had a variable also named cast
   - Some files had not included a header file that defines the cast
     functions
   - Some files are definitions of the classes that have the casting
     methods, so the code still refers to the method instead of the
     function without adding a prefix or removing the method declaration
     at the same time.

```
ninja -C $BUILD_DIR clang-tidy

run-clang-tidy -clang-tidy-binary=$BUILD_DIR/bin/clang-tidy -checks='-*,misc-cast-functions'\
               -header-filter=mlir/ mlir/* -fix

rm -rf $BUILD_DIR/tools/mlir/**/*.inc

git restore mlir/lib/IR mlir/lib/Dialect/DLTI/DLTI.cpp\
            mlir/lib/Dialect/Complex/IR/ComplexDialect.cpp\
            mlir/lib/**/IR/\
            mlir/lib/Dialect/SparseTensor/Transforms/SparseVectorization.cpp\
            mlir/lib/Dialect/Vector/Transforms/LowerVectorMultiReduction.cpp\
            mlir/test/lib/Dialect/Test/TestTypes.cpp\
            mlir/test/lib/Dialect/Transform/TestTransformDialectExtension.cpp\
            mlir/test/lib/Dialect/Test/TestAttributes.cpp\
            mlir/unittests/TableGen/EnumsGenTest.cpp\
            mlir/test/python/lib/PythonTestCAPI.cpp\
            mlir/include/mlir/IR/
```

Differential Revision: https://reviews.llvm.org/D150123

Vector dialect patterns have grown enormously in the past year to a point where they are now impenetrable.
Start reorganizing them towards finer-grained control.

Differential Revision: https://reviews.llvm.org/D146736