assert(isValidDesktopFileKey("Generic-Name"));
assert(isValidDesktopFileKey("Generic-Name[ru_RU]"));
assert(!isValidDesktopFileKey("Name$"));
assert(!isValidDesktopFileKey(""));
assert(!isValidDesktopFileKey("[ru_RU]"));
assert(!isValidDesktopFileKey("Name[ru\nRU]"));
Test whether the string is valid key in terms of Desktop File Specification.
Not actually used in inilike.file.IniLikeFile, but can be used in derivatives. Only the characters A-Za-z0-9- may be used in key names. Note: this function automatically separate key from locale. Locale is validated against isValidKey.