ICU format support for pseudolocalizes.

Custom parser can handle nested ICU messages even if they
are split into multiple fragments. Code reworked to encapsulate
all pseudolocalization logic in Pseudolocalizer and PseudoMethods
classes. To minimize a changelist size, some static functions
remained. Fake BiDi pseudolocalization method is reimplemented
to handle word boundaries correctly. Unit tests added.

(cherry picked from commit cbb1e676)

bug: 22060509

Change-Id: I11968d81984d99501a4d9334ff2e7453a1eb7a00