transliterate option of test_language plugin should not modify printf() parameter fields

[li-dl]

I have a string which has been extracted from C++ code which uses printf() parameter fields: https://en.wikipedia.org/wiki/Printf_format_string#Parameter_field

The transliterate option of the test_language plugin in Serge v1.4 is modifying the format sub-strings when they should be left as-is.

Location	String
C++ code	Showing %1$d of %2$d instruments
Actual Serge output	Šĥőŵĩŋğ %1$đ őḟ %2$đ ĩŋšţŕũḿēŋţš
Desired Serge output	Šĥőŵĩŋğ %1$d őḟ %2$d ĩŋšţŕũḿēŋţš

i.e. The d type field should not be changed to đ