TokenProcessor - Allow basic filter/modifier expressions

TokenProcessor - Allow basic filter/modifier expressions

Before
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`Hello {foo.bar}`

After
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`Hello {foo.bar|upper}` and `Hello {foo.bar|lower}`

Technical Details
-----------------

This only supports tokens that supply values through `civi.token.eval`.  At the time of
this commit, most `{contact.*}` tokens still use `TokenCompatSubscriber::onRender()` to
hack-in their values and won't work until they switch over.

The regex which recognizes the filter is pretty tight (`\w+`).  This can be relaxed
somewhat by a subsequent change, but I'd say such a change has a burden to demonstrate
safety/interoparbility when running in Token-Smarty format.  (e.g.  demonstrate that
matching of open/close symbols works correctly).