Truncate tag filter descriptions

Truncate tag filter descriptions

Introduce truncateInternal() method in Language class, based on
existing truncate() method. New method abstracts string truncation,
allowing users to specify callable functions for text length measurement
and string truncation.

New method, truncateInternal(), is used to provide two options for
text truncation:
* For DB usage: truncateForDatabase() method is truncating text by
number of bytes.
* For UI usage: truncateForVisual() method is truncating text by number
of characters, using multibyte string PHP methods.

Old truncate() method is deprecated and just returns the results of
truncateForDatabase() method.

Newly introduced truncateForVisual() method is used for
truncation of long tag descriptions in RCFilters menu.

Bug: T179626
Change-Id: Ib01a8c303304064dde3ce983b817d93a88a5affd