Add translation context for statistical "Error"

Add translation context for statistical "Error"

Since gnulib's gettext.h defines pgettext() as macro with string
catenation, it's impossible to add pgettext version API for
pivot_value_new_text().  Rather, the pivot_value creation part is
split into pivot_value_new_text_translate() and let's expand
pgettext() upon calling it.

With this, C_() and NC_() macros are defined for translation with
context.

Fixing bug #66244.