Allow defining local labels for another scope (#1159)

fix #1157 for the following source code

```
section "hSAVE_locals",HRAM
func3.hSpam: ds 1  ; no longer produces an error
;.hEggs: ds 1      ; uncomment this to see the new error

section "demo",ROM0
func3:
  ldh a, [.hSpam]
  ret
```

Remove two errors:
- `Not currently in the scope of 'func3'`
- `Local label 'func3.hSpam' in main scope`

Add one error:
- `Relative local label '.hSpam' in main scope`

Co-authored-by: Rangi <35663410+Rangi42@users.noreply.github.com>

test/asm/sym-scope.asm

@@ -1,8 +1,9 @@
 SECTION "Scopes", ROM0
 
-; Neither of these should be created
-.tooSoon
-Nice.try
+; Tests of injecting local labels into another label's scope.
+; This construction is useful to define a subroutine's local variables
+; in WRAM or HRAM.
+Valid.syntax
 
 Parent:
 .loc
@@ -11,8 +12,8 @@ Parent.explicit
 	dw .explicit ; This should expand to the above
 
 
-; None of the two locals below should manage to be created, being in the wrong scopes
-; Note however that `Parentheses` begins with `Parent`, which string checks may fail to handle
+; Note that `Parentheses` begins with `Parent`,
+; which string checks may fail to handle
 
 Parentheses.check