chore(common): handle an empty <transformGroup/> properly

- difference in fast-xml-parser and xml2js handling here
- part of the move to fast-xml-parser

Fixes: #12208

developer/src/common/web/utils/src/types/ldml-keyboard/ldml-keyboard-xml-reader.ts

@@ -104,6 +104,14 @@ export class LDMLKeyboardXMLSourceFileReader {
     if(source?.keyboard3?.transforms) {
       for(const transforms of source.keyboard3.transforms)  {
         boxXmlArray(transforms, 'transformGroup');
+        // need to see if there's an empty ('') element.
+        // the schema allows an empty object, but the spec doesn't.
+        for (let i=0; i<transforms.transformGroup.length; i++) {
+          if (transforms.transformGroup[i] === '') {
+            // substitute empty object. the compiler will complain about it.
+            transforms.transformGroup[i] = { };
+          }
+        }
         for (const transformGroup of transforms.transformGroup) {
           boxXmlArray(transformGroup, 'transform');
           boxXmlArray(transformGroup, 'reorder');