When using test-kind=2 in the bytecode roundtrip test, integer types
(i32) are replaced by a custom type (TestI32Type) via a type callback.
This exposed two crash scenarios:
1. Reading IntegerAttr with an unsupported type: `getIntegerBitWidth`
returns 0 for unsupported types and emits an error, but
`readAPIntWithKnownWidth` would proceed to call
`reader.readAPIntWithKnownWidth(0)`, creating a zero-width APInt with a
potentially non-zero value. Fix: early-return failure when `bitWidth ==
0`.
2. Reading VectorType with an unsupported element type:
`VectorType::get` asserts that the element type implements
VectorElementTypeInterface. When the element type is replaced by a
custom type that doesn't implement this interface, the program crashes.
Fix: use `VectorType::getChecked` with a diagnostic emitter lambda
instead of `get<VectorType>` in the bytecode builder.
Fixes#128312
e904d559c5