Vector: Implement find, find_if, find_first_matching in terms of AK::find*

Problem:
- The implementation of `find` is coupled to the implementation of `Vector`.
- `Vector::find` takes the predicate by value which might be expensive.

Solution:
- Decouple the implementation of `find` from `Vector` by using a
  generic `find` algorithm.
- Change the name of `find` with a predicate to `find_if` so that a
  binding reference can be used and the predicate can be forwarded to
  avoid copies.
- Change all the `find(pred)` call sites to use `find_if`.

Applications/SystemMonitor/DevicesModel.cpp

@@ -182,7 +182,7 @@ void DevicesModel::update()
             unsigned _major = major(statbuf.st_rdev);
             unsigned _minor = minor(statbuf.st_rdev);
 
-            auto it = m_devices.find([_major, _minor](auto& device_info) {
+            auto it = m_devices.find_if([_major, _minor](const auto& device_info) {
                 return device_info.major == _major && device_info.minor == _minor;
             });
             if (it != m_devices.end()) {