Update XMB placeholders(<ph>) to include the original value on top of an
example. Placeholders can by definition have one example(<ex>) tag and a
text node. The text node is used by TC as the "original" value from the
placeholder, while the example should represent a dummy value.
For example: <ph name="PET"><ex>Gopher</ex>{{ petName }}</ph>.
This change makes sure that we have the original text, but it *DOES NOT*
make sure that the example is correct. The example has the same wrong
behavior of showing the interpolation text rather than a useful
example.
No breaking changes, but tools that depend on the previous behavior and
don't consider the full XMB definition may fail to parse the XMB.
Fixes b/72565847
PR Close#25079
Carlos Ortiz Garcia
Misko Hevery
Olivier Combe
Jason Aden