BUG-1275: optimize TypeDefinitionAwareCodec.normalizeHexadecimal()

normalizeHexadecimal() used non-optimal combination of searching for a
substring and a non-compiled regex replace. Optimize this by using
a precomputed CharMatcher instead.

Change-Id: Ie388735244c779d0e80ed98d8c6ce71bf2f4fbf6
Signed-off-by: Robert Varga <rovarga@cisco.com>