tests: Add the capi.object miss handle support to the capi.mouse shim

tests/examples/shims/mouse.lua

@@ -3,7 +3,6 @@ local screen = require("screen")
 local coords = {x=100,y=100}
 
 local mouse = {
-    screen  = screen[1],
     old_histories = {},
     history       = {},
 }
@@ -17,11 +16,35 @@ function mouse.coords(args)
     return coords
 end
 
+function mouse.set_newindex_miss_handler(h)
+    rawset(mouse, "_ni_handler", h)
+end
+
+function mouse.set_index_miss_handler(h)
+    rawset(mouse, "_i_handler", h)
+end
+
 function mouse.push_history()
     table.insert(mouse.old_histories, mouse.history)
     mouse.history = {}
 end
 
-return mouse
+return setmetatable(mouse, {
+    __index = function(self, key)
+        if key == "screen" then
+            return screen[1]
+        end
+        local h = rawget(mouse,"_i_handler")
+        if h then
+            return h(self, key)
+        end
+    end,
+    __newindex = function(...)
+        local h = rawget(mouse,"_ni_handler")
+        if h then
+            h(...)
+        end
+    end,
+})
 
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