Function apply_transform

subprojects/llama.cpp/common/jinja/string.cpp:116–121

using transform_fn = std::function<std::string(const std::string&)>;
static string apply_transform(string & self, const transform_fn & fn) {
    for (auto & part : self.parts) {
        part.val = fn(part.val);
    }
    return self;
}

string string::uppercase() {
    return apply_transform(*this, [](const std::string & s) {