fix(semantic): flag function expressions with SymbolFlags::Function (#2891)

# What This PR Does

Consider the following code snippet

```js
const x = function y () {{
```

`y` will now be flagged with `SymbolFlags::Function`. This follow's
tsc's behavior.

- [Example in OXC
Playground](https://oxc-project.github.io/oxc/playground/?code=3YCAAICagICAgICAgICxG0qZRraXZOpcCHVsSRwDq2kRR0HprsTfRRT5WMw%2Ff2epoIA%3D)
- [Example in TypeScript AST
Viewer](https://ts-ast-viewer.com/#code/MYewdgzgLgBAHjAvDAZgVzMKBLcMCeAFAJQwDeAvgFBA)

crates/oxc_semantic/src/binder.rs

@@ -146,7 +146,7 @@ impl<'a> Binder for Function<'a> {
                 let symbol_id = builder.declare_symbol(
                     ident.span,
                     &ident.name,
-                    SymbolFlags::empty(),
+                    SymbolFlags::Function,
                     SymbolFlags::empty(),
                 );
                 ident.symbol_id.set(Some(symbol_id));

crates/oxc_semantic/tests/symbols.rs

@@ -26,6 +26,18 @@ fn test_function_simple() {
         .test();
 }
 
+#[test]
+fn test_function_expressions() {
+    SemanticTester::js("const x = function y() {}")
+        .has_some_symbol("y")
+        .contains_flags(SymbolFlags::Function)
+        .test();
+    SemanticTester::js("const x = () => {}")
+        .has_some_symbol("x")
+        .contains_flags(SymbolFlags::BlockScopedVariable | SymbolFlags::ConstVariable)
+        .test();
+}
+
 #[test]
 fn test_var_simple() {
     SemanticTester::js("let x; { let y; }")