feat(wm): add active window border

This commit adds an optional active window border with a user-defined
colour. This is achieved by spawning a dedicated "border window" and
constantly placing it behind the focused window, or hiding it whenever
necessary.

Some constraints to note:

- The border will only be applied to windows managed by komorebi
- This means that if you temporarily float a window, it will lose the
  active window border
- There are some issues where parts of the border will be broken by
  applications like Zoom, even if Zoom is behind the currently focused
  window
- You probably want to turn off window shadows globally in Advanced
  System Settings -> Performance for the borders to have a consistent
  colour all the way around the window
- There is some inevitable jank due to trying to reposition both the
  focused window and the "border window" behind it simultaneously
- There are no borders for unfocused windows

resolve #182

Cargo.lock

@@ -494,6 +494,7 @@ dependencies = [
  "lazy_static",
  "miow 0.4.0",
  "nanoid",
+ "os_info",
  "parking_lot",
  "paste",
  "schemars",
@@ -760,6 +761,17 @@ version = "1.13.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "18a6dbe30758c9f83eb00cbea4ac95966305f5a7772f3f42ebfc7fc7eddbd8e1"
 
+[[package]]
+name = "os_info"
+version = "3.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0eca3ecae1481e12c3d9379ec541b238a16f0b75c9a409942daa8ec20dbfdb62"
+dependencies = [
+ "log",
+ "serde",
+ "winapi 0.3.9",
+]
+
 [[package]]
 name = "os_str_bytes"
 version = "6.2.0"