[CIR] Add support for complex cast operations

[Lancern]

This PR adds support for complex cast operations. It adds the following new cast kind variants to the cir.cast operation:

• float_to_complex,
• int_to_complex,
• float_complex_to_real,
• int_complex_to_real,
• float_complex_to_bool,
• int_complex_to_bool,
• float_complex,
• float_complex_to_int_complex,
• int_complex, and
• int_complex_to_float_complex.

CIRGen and LLVM IR support for these new cast variants are also included.

[Lancern]

Rebased onto the latest main.

[Lancern]

Rebased onto the latest main.