zig fmt: remove trailing whitespace on doc comments

Fixes #11353

The renderer treats comments and doc comments differently since doc
comments are parsed into the Ast. This commit adds a check after getting
the text for the doc comment and trims whitespace at the end before
rendering.

The `a = 0,` in the test is here to avoid a ParseError while parsing the
test.

lib/std/zig/parser_test.zig

@@ -4712,6 +4712,28 @@ test "zig fmt: space after top level doc comment" {
     );
 }
 
+test "zig fmt: remove trailing whitespace after container doc comment" {
+    try testTransform(
+        \\//! top level doc comment 
+        \\
+    ,
+        \\//! top level doc comment
+        \\
+    );
+}
+
+test "zig fmt: remove trailing whitespace after doc comment" {
+    try testTransform(
+        \\/// doc comment 
+        \\a = 0,
+        \\
+    ,
+        \\/// doc comment
+        \\a = 0,
+        \\
+    );
+}
+
 test "zig fmt: for loop with ptr payload and index" {
     try testCanonical(
         \\test {