[LiveComponent] Tokenize classes on all allowed whitespaces

The class attribute can be tokenized by any white space as defined by
the HTML spec. A class string containing new lines was not correctly
cleaned / trimmed, resulting in incorrectly detected class changes and a
browser error if empty classes or classes with newlines were applied.

Fixes #1819

src/LiveComponent/assets/src/Rendering/ExternalMutationTracker.ts

@@ -190,19 +190,18 @@ export default class {
         const element = mutation.target as Element;
 
         const previousValue = mutation.oldValue;
-        const previousValues = previousValue ? previousValue.split(' ') : [];
+        const previousValues = previousValue ? previousValue.trim().split(' ') : [];
+        const previousValuesClean = [];
         previousValues.forEach((value, index) => {
             const trimmedValue = value.trim();
             if (trimmedValue !== '') {
-                previousValues[index] = trimmedValue;
-            } else {
-                previousValues.splice(index, 1);
+                previousValuesClean.push(trimmedValue);
             }
         });
 
         const newValues: string[] = [].slice.call(element.classList);
-        const addedValues = newValues.filter((value) => !previousValues.includes(value));
-        const removedValues = previousValues.filter((value) => !newValues.includes(value));
+        const addedValues = newValues.filter((value) => !previousValuesClean.includes(value));
+        const removedValues = previousValuesClean.filter((value) => !newValues.includes(value));
 
         addedValues.forEach((value) => {
             elementChanges.addClass(value);