Rename @Register to @RegisterDescriptor

[fumoboy007]

(I originally proposed this change here.)

---

The @Register macro is used like so:

@Register(bitWidth: 32)
struct CR1 {
  @ReadOnly(bits: 0..<1)
  var en: Bool
  @WriteOnly(bits: 1..<2)
  var clken: Bool
}

The @Register macro generates Read and Write structs using the properties of the given struct. Those generated structs are the ones that will be read from or written to. I think the macro name @Register is a little misleading because it is those generated structs that will be read from or written to, not the given struct.

By contrast, the Register struct is well-named. The struct is initialized with the memory address of the register and provides the caller with an API to access the Read/Write structs that were generated from the @Register struct:

var cr1 = Register<CR1>(unsafeAddress: 0x1000)
cr1.modify { (read, write) in
  print(read.en)
  write.clken = true
}

I propose renaming @Register to @RegisterDescriptor to make it clear that the struct is only used to describe the register and that one still needs to use the Register struct (with the @RegisterDescriptor type as a generic type parameter) to access the register’s memory.