test/cases/0160-string: conform coding guidelines
test/cases/0160-string: add tests and ldoc description for fill_placeholders_ex
test/cases/0160-string: format code to conform coding guidelines
lua-nucleo/string: add ldoc description for fill_placeholders
test/cases/0160-string: add tests and ldoc description for
fill_curly_placeholders
test/cases/0160-string: add tests and ldoc description for split_by_char
test/cases/0160-string: add tests and ldoc description for split_by_offset
test/cases/0160-string: add tests, ldoc description and small fix to prevent infinite loop for count_substrings
test/cases/0160-string: add tests and ldoc description for kv_concat
test/cases/0160-string: add tests for escape_for_json
test/cases/0160-string: add tests and ldoc description for
get_escaped_chars_in_ranges