Compound Expressions sometimes wrongly refer to Primary Expressions

I think the following rules are supposed to refer to `compound-expr` rather than `primary-expr`:

```
labeled-member-expr ::=
primary-expr '.' primary-decl-ref

indexed-member-expr ::=
primary-expr '.' member-index
```
```
function-call-head ::= (no-implicit-whitespace)
primary-expr '('
```
```
subscript-call-head ::= (no-implicit-whitespace)
primary-expr '['
```

Search the specification for the four quoted productions: labeled-member-expr, indexed-member-expr, function-call-head, and subscript-call-head. Compare their expression references with the surrounding grammar and verify whether compound-expr is intended; done means the affected rules consistently use the correct expression category.

Written by the indexing model from the issue text.