This patch changes the behavior of `convert-to-llvm{dynamic=true}` so
that the nearest `DataLayout` is used to configure LowerToLLVMOptions
and LLVMTypeConverter.

Example:

```mlir
module attributes {dlti.dl_spec = #dlti.dl_spec<#dlti.dl_entry<index, 16>>} {
  func.func private @test_16bit_index(%arg0: index) -> index
}
// mlir-opt --convert-to-llvm="dynamic=true"
module attributes {dlti.dl_spec = #dlti.dl_spec<index = 16 : i64>} {
  llvm.func @test_16bit_index(i16) -> i16 attributes {sym_visibility = "private"}
}
```

This commit improves the `allowPatternRollback` flag handling in the
dialect conversion driver. Previously, this flag was used to merely
detect cases that are incompatible with the new One-Shot Dialect
Conversion driver. This commit implements the driver itself: when the
flag is set to "false", all IR changes are materialized immediately,
bypassing the `IRRewrite` and `ConversionValueMapping` infrastructure.

A few selected test cases now run with both the old and the new driver.

RFC:
https://discourse.llvm.org/t/rfc-a-new-one-shot-dialect-conversion-driver/79083

These are identified by misc-include-cleaner.  I've filtered out those
that break builds.  Also, I'm staying away from llvm-config.h,
config.h, and Compiler.h, which likely cause platform- or
compiler-specific build failures.

`let constructor` is deprecated since the table gen backend emits most
of the glue logic to build a pass. This PR retires the td method for
most (I need another pass) passes in the Conversion directory.

This patch adds the `ConvertToLLVMAttrInterface` and
`ConvertToLLVMOpInterface` interfaces. It also modifies the
`convert-to-llvm` pass to use these interfaces when available.

The `ConvertToLLVMAttrInterface` interfaces allows attributes to
configure conversion to LLVM, including the conversion target, LLVM type
converter, and populating conversion patterns. See the `NVVMTargetAttr`
implementation of this interface for an example of how this interface
can be used to configure conversion to LLVM.

The `ConvertToLLVMOpInterface` interface collects all convert to LLVM
attributes stored in an operation.

Finally, the `convert-to-llvm` pass was modified to use these interfaces
when available. This allows applying `convert-to-llvm` to GPU modules
and letting the `NVVMTargetAttr` decide which patterns to populate.

`PassManager::run` loads the dependent dialects for each pass into the
current context prior to invoking the individual passes. If the
dependent dialect is already loaded into the context, this should be a
no-op. However, if there are extensions registered in the
`DialectRegistry`, the dependent dialects are unconditionally registered
into the context.

This poses a problem for dynamic pass pipelines, however, because they
will likely be executing while the context is in an immutable state
(because of the parent pass pipeline being run).

To solve this, we'll update the extension registration API on
`DialectRegistry` to require a type ID for each extension that is
registered. Then, instead of unconditionally registered dialects into a
context if extensions are present, we'll check against the extension
type IDs already present in the context's internal `DialectRegistry`.
The context will only be marked as dirty if there are net-new extension
types present in the `DialectRegistry` populated by
`PassManager::getDependentDialects`.

Note: this PR removes the `addExtension` overload that utilizes
`std::function` as the parameter. This is because `std::function` is
copyable and potentially allocates memory for the contained function so
we can't use the function pointer as the unique type ID for the
extension.

Downstream changes required:
- Existing `DialectExtension` subclasses will need a type ID to be
registered for each subclass. More details on how to register a type ID
can be found here:
https://github.com/llvm/llvm-project/blob/8b68e06731e0033ed3f8d6fe6292ae671611cfa1/mlir/include/mlir/Support/TypeID.h#L30
- Existing uses of the `std::function` overload of `addExtension` will
need to be refactored into dedicated `DialectExtension` classes with
associated type IDs. The attached `std::function` can either be inlined
into or called directly from `DialectExtension::apply`.

---------

Co-authored-by: Mehdi Amini <joker.eph@gmail.com>

This is a follow-up to the introduction of `convert-to-llvm`: it is
supposed to be a unifying pass through the
`ConvertToLLVMPatternInterface`, but some specific conversion (like the
GPU target) aren't vanilla LLVM target. Instead they need extra
customizations that are specific to LLVM-on-GPUs and our custom runtime
wrappers.
This change make the GpuToLLVMConversionPass just as pluggable as the
`convert-to-llvm` by using the same mechanism.

virtual is redundant if method is final.