fix rename/references missing asm output operands

[DaliVana]

Fixes #3222

Renaming a variable did not update its occurrence inside an inline asm output operand:

pub fn main() void {
    var bar = 5;
    asm volatile (
        \\ mov $5, %rax
        : [ret] "={rax}" (bar), // <-- not renamed
    );
}

The same occurrence was also missing from textDocument/references and textDocument/documentHighlight.

Cause
In the grammar, an asm output operand without -> is a bare IDENTIFIER — parseAsmOutputItem consumes the token and creates no AST node for it (only the -> type form stores a node). Reference collection (Builder.referenceNode) walks AST nodes, so the operand token was invisible. Asm inputs work because their operand is a full expression node yielded by the child iterator (#1142); outputs with -> likewise.

Fix
Handle .asm_simple/.@"asm" in Builder.referenceNode: for each output item, the operand token is nodeMainToken(output) + 4 (the same layout already relied on in semantic_tokens.zig and the ChildIterator). The -> T form is skipped (already covered as a child node). The operand then goes through the same treatment as the .identifier case: the _/primitive/escaped-identifier guard, lookupSymbolGlobal, alias resolution, and target_symbol.eql — added per matching output, so multiple outputs referencing the same variable all get collected.

This fixes rename, find-references, and document highlight in one place, since all three share symbolReferences.

Tests
Five new cases in test "asm":

• plain output operand (the issue's repro shape)
• two outputs referencing the same variable
• arrow-form and plain-form output mixed in one asm (guards the skip logic)
• container-level var shadowed by a same-named local used in an asm operand — must not be reported for the container decl (exercises the symbol-identity check negatively)
• const @"i32" with a bare (i32) operand — must not be reported (asm analogue of the existing escaped-identifier-vs-primitive test)
• The negative tests were mutation-verified: removing the primitive guard or neutralizing the eql check each makes the suite fail.