[mlir][Transforms][NFC] Dialect Conversion: Move argument materialization logic (#96329)

This commit moves the argument materialization logic from
`legalizeConvertedArgumentTypes` to
`legalizeUnresolvedMaterializations`.

Before this change:
- Argument materializations were created in
`legalizeConvertedArgumentTypes` (which used to call
`materializeLiveConversions`).

After this change:
- `legalizeConvertedArgumentTypes` creates a "placeholder"
`unrealized_conversion_cast`.
- The placeholder `unrealized_conversion_cast` is replaced with an
argument materialization (using the type converter) in
`legalizeUnresolvedMaterializations`.
- All argument and target materializations now take place in the same
location (`legalizeUnresolvedMaterializations`).

This commit brings us closer towards creating all source/target/argument
materializations in one central step, which can then be made optional
(and delegated to the user) in the future. (There is one more source
materialization step that has not been moved yet.)

This commit also consolidates all `build*UnresolvedMaterialization`
functions into a single `buildUnresolvedMaterialization` function.

0 files changed, 0 insertions, 0 deletions