LowerForAndIf: expand affine_apply's inplace

Existing implementation was created before ML/CFG unification refactoring and
did not concern itself with further lowering to separate concerns.  As a
result, it emitted `affine_apply` instructions to implement `for` loop bounds
and `if` conditions and required a follow-up function pass to lower those
`affine_apply` to arithmetic primitives.  In the unified function world,
LowerForAndIf is mostly a lowering pass with low complexity.  As we move
towards a dialect for affine operations (including `for` and `if`), it makes
sense to lower `for` and `if` conditions directly to arithmetic primitives
instead of relying on `affine_apply`.

Expose `expandAffineExpr` function in LoweringUtils.  Use this function
together with `expandAffineMaps` to emit primitives that implement loop and
branch conditions directly.

Also remove tests that become unnecessary after transforming LowerForAndIf into
a function pass.

PiperOrigin-RevId: 227563608