seek-to: Retrieve clipboard content natively

It's been some time since mpv implemented native clipboard access on all
platforms. The old method of retriving clipboard content using external
subprocesses is only used as a fallback now, removing complex code.
The implementation is shamelessly copied from mpv's console.lua script:
https://github.com/mpv-player/mpv/blob/d837c43656876fb2fb7cbcf7e74bd438ba563217/player/lua/console.lua#L1329-L1358
Though to simplify the code further, I didn't add support for the
primary clipboard in X11 and Wayland.

Author: dexeonify

scripts/seek-to.lua

@@ -240,36 +240,33 @@ function set_inactive()
     active = false
 end
 
-function subprocess(args)
-    local cmd = {
-        name = "subprocess",
-        args = args,
-        playback_only = false,
-        capture_stdout = true
-    }
-    local res = mp.command_native(cmd)
-    if not res.error then
-        return res.stdout
-    else
-        msg.error("Error getting data from clipboard")
-        return
-    end
-end
-
-function get_clipboard()
-    local res
-    if platform == "windows" then
-        res = subprocess({ "powershell", "-Command", "Get-Clipboard", "-Raw" })
-    elseif platform == "darwin" then
-        res = subprocess({ "pbpaste" })
-    elseif platform == "linux" then
-        if os.getenv("WAYLAND_DISPLAY") then
-            res = subprocess({ "wl-paste", "-n" })
-        else
-            res = subprocess({ "xclip", "-selection", "clipboard", "-out" })
+local function get_clipboard()
+    if platform == "x11" then
+        local res = utils.subprocess({
+            args = { "xclip", "-selection", "clipboard", "-out" },
+            playback_only = false,
+        })
+        if not res.error then
+            return res.stdout
+        end
+    elseif platform == "wayland" then
+        if mp.get_property("current-clipboard-backend") == "wayland" then
+            return mp.get_property("clipboard/text", "")
+        end
+        -- Wayland VO clipboard is only updated on window focus
+        if get_property_cached("focused") then
+            return mp.get_property("clipboard/text", "")
+        end
+        local res = utils.subprocess({
+            args = { "wl-paste", "-n" },
+            playback_only = false,
+        })
+        if not res.error then
+            return res.stdout
         end
+    elseif platform == "windows" or platform == "darwin" then
+        return mp.get_property("clipboard/text", "")
     end
-    return res
 end
 
 function paste_timestamp()