fix(es/react): Fix handling of whitespaces (#6935)

**Related issue:**

 - Closes #6931.

Author: kdy1

crates/swc_ecma_transforms_react/src/jsx/mod.rs

@@ -1336,15 +1336,19 @@ fn count_children(children: &[JSXElementChild]) -> usize {
 fn transform_jsx_attr_str(v: &str) -> String {
     let single_quote = false;
     let mut buf = String::with_capacity(v.len());
+    let mut iter = v.chars().peekable();
 
-    for c in v.chars() {
+    while let Some(c) = iter.next() {
         match c {
             '\u{0008}' => buf.push_str("\\b"),
             '\u{000c}' => buf.push_str("\\f"),
-            ' ' | '\n' | '\r' | '\t' => {
-                if buf.ends_with(' ') {
-                } else {
-                    buf.push(' ')
+            ' ' => buf.push(' '),
+
+            '\n' | '\r' | '\t' => {
+                buf.push(' ');
+
+                while let Some(' ') = iter.peek() {
+                    iter.next();
                 }
             }
             '\u{000b}' => buf.push_str("\\v"),

crates/swc_ecma_transforms_react/tests/jsx/fixture/issue-6931/input.js

@@ -0,0 +1,2 @@
+const f1 = <Component on={"    "} />
+const f2 = <Component on="    " />

crates/swc_ecma_transforms_react/tests/jsx/fixture/issue-6931/output.mjs

@@ -0,0 +1,6 @@
+const f1 = /*#__PURE__*/ React.createElement(Component, {
+    on: "    "
+});
+const f2 = /*#__PURE__*/ React.createElement(Component, {
+    on: "    "
+});