Replace `getAsInteger()` parsing of the `patchable-function-entry`
and `patchable-function-prefix` function attributes with the existing
`Function::getFnAttributeAsParsedInteger()` helper across AsmPrinter
and all backend targets.
The IR verifier already validates these attributes as unsigned base-10
integers via `checkUnsignedBaseTenFuncAttr`, so parse failure at point
of use indicates a verifier bypass or IR corruption.
`getFnAttributeAsParsedInteger()` returns a default of 0 on failure
(matching the implicit behavior of the old code) and emits a diagnostic
rather than silently continuing.
766a42a11c