fix(es/codegen): Fix ascii_only for identifiers

crates/swc/tests/fixture/issues-8xxx/8260/output/1.js

@@ -1,2 +1,2 @@
-function p(\xb5, \u03C3) {}
+function p(\u00b5, \u03C3) {}
 console.log(p);

crates/swc/tests/fixture/issues-8xxx/8852/input/.swcrc

@@ -0,0 +1,21 @@
+{
+    "jsc": {
+        "parser": {
+            "syntax": "ecmascript",
+            "jsx": false
+        },
+        "target": "es3",
+        "loose": false,
+        "minify": {
+            "compress": false,
+            "format": {
+                "asciiOnly": true
+            }
+        }
+    },
+    "module": {
+        "type": "es6"
+    },
+    "minify": false,
+    "isModule": true
+}

crates/swc/tests/fixture/issues-8xxx/8852/input/1.js

@@ -0,0 +1,2 @@
+const módulo = 123;
+console.log(módulo);

crates/swc/tests/fixture/issues-8xxx/8852/input/2.js

@@ -0,0 +1,2 @@
+const m\u00f3dulo = 123;
+console.log(m\u00f3dulo);

crates/swc/tests/fixture/issues-8xxx/8852/output/1.js

@@ -0,0 +1,2 @@
+var m\u00f3dulo = 123;
+console.log(m\u00f3dulo);

crates/swc/tests/fixture/issues-8xxx/8852/output/2.js

@@ -0,0 +1,2 @@
+var m\u00f3dulo = 123;
+console.log(m\u00f3dulo);

crates/swc_ecma_codegen/src/lib.rs

@@ -3871,7 +3871,12 @@ fn get_ascii_only_ident(sym: &str, may_need_quote: bool, target: EsVersion) -> C
     while let Some(c) = iter.next() {
         match c {
             '\x00' => {
-                buf.push_str("\\x00");
+                if may_need_quote {
+                    need_quote = true;
+                    let _ = write!(buf, "\\x00");
+                } else {
+                    let _ = write!(buf, "\\u0000");
+                }
             }
             '\u{0008}' => buf.push_str("\\b"),
             '\u{000c}' => buf.push_str("\\f"),
@@ -3959,20 +3964,31 @@ fn get_ascii_only_ident(sym: &str, may_need_quote: bool, target: EsVersion) -> C
                 buf.push('"');
             }
             '\x01'..='\x0f' if !first => {
-                let _ = write!(buf, "\\x0{:x}", c as u8);
+                if may_need_quote {
+                    need_quote = true;
+                    let _ = write!(buf, "\\x{:x}", c as u8);
+                } else {
+                    let _ = write!(buf, "\\u00{:x}", c as u8);
+                }
             }
             '\x10'..='\x1f' if !first => {
-                let _ = write!(buf, "\\x{:x}", c as u8);
+                if may_need_quote {
+                    need_quote = true;
+                    let _ = write!(buf, "\\x{:x}", c as u8);
+                } else {
+                    let _ = write!(buf, "\\u00{:x}", c as u8);
+                }
             }
             '\x20'..='\x7e' => {
                 buf.push(c);
             }
             '\u{7f}'..='\u{ff}' => {
                 if may_need_quote {
                     need_quote = true;
+                    let _ = write!(buf, "\\x{:x}", c as u8);
+                } else {
+                    let _ = write!(buf, "\\u00{:x}", c as u8);
                 }
-
-                let _ = write!(buf, "\\x{:x}", c as u8);
             }
             '\u{2028}' => {
                 buf.push_str("\\u2028");