Update the url rewriter to work with Guava >= 26.0

Guava 19.0 introduced CharMatcher.ascii() as alternative for the constant ASCII. ASCII was deprecated.

The deprecated ASCII constant is removed from the CharMatcher class in Guava 26.0

As url rewriter specs Guava 19.0 but since v13 we use 27.0 ASCII no longer works.

Code can be updated to use ascii() but then the code will not work with v10.2 and v11.2 that provide Guava 16.0.

To remove the dependency on a specific version of Guava the CharMatcher methods can be copied to the url rewriter code. If we decide to bump all releases to the latest Guava we can remove the duplicated code can be replaced with ascii() from Guava