stats.lua: use fixed naming for single invocation key bindings

The names of single invocation key bindings for specific pages will be
changed if defines user key bindings, then original invocation fails.

e.g. : when user defines `key_page_4=F4`, then key binding name
`stats/display-page-4-toggle`
becomes
`stats/display-page-F4-toggle`,
and OSC menu `Help` fails.

player/lua/stats.lua

@@ -1431,12 +1431,12 @@ cache_recorder_timer:kill()
 -- Current page and <page key>:<page function> mapping
 curr_page = o.key_page_1
 pages = {
-    [o.key_page_1] = { f = default_stats, desc = "Default" },
-    [o.key_page_2] = { f = vo_stats, desc = "Extended Frame Timings", scroll = true },
-    [o.key_page_3] = { f = cache_stats, desc = "Cache Statistics" },
-    [o.key_page_4] = { f = keybinding_info, desc = "Active Key Bindings", scroll = true },
-    [o.key_page_5] = { f = track_info, desc = "Selected Tracks Info", scroll = true },
-    [o.key_page_0] = { f = perf_stats, desc = "Internal Performance Info", scroll = true },
+    [o.key_page_1] = { idx = 1, f = default_stats, desc = "Default" },
+    [o.key_page_2] = { idx = 2, f = vo_stats, desc = "Extended Frame Timings", scroll = true },
+    [o.key_page_3] = { idx = 3, f = cache_stats, desc = "Cache Statistics" },
+    [o.key_page_4] = { idx = 4, f = keybinding_info, desc = "Active Key Bindings", scroll = true },
+    [o.key_page_5] = { idx = 5, f = track_info, desc = "Selected Tracks Info", scroll = true },
+    [o.key_page_0] = { idx = 0, f = perf_stats, desc = "Internal Performance Info", scroll = true },
 }
 
 
@@ -1720,17 +1720,17 @@ mp.add_key_binding(nil, "display-stats", function() process_key_binding(true) en
 mp.add_key_binding(nil, "display-stats-toggle", function() process_key_binding(false) end,
     {repeatable=false})
 
-for k, _ in pairs(pages) do
+for k, page in pairs(pages) do
     -- Single invocation key bindings for specific pages, e.g.:
     -- "e script-binding stats/display-page-2"
-    mp.add_key_binding(nil, "display-page-" .. k, function()
+    mp.add_key_binding(nil, "display-page-" .. page.idx, function()
         curr_page = k
         process_key_binding(true)
     end, {repeatable=true})
 
     -- Key bindings to toggle a specific page, e.g.:
     -- "h script-binding stats/display-page-4-toggle".
-    mp.add_key_binding(nil, "display-page-" .. k .. "-toggle", function()
+    mp.add_key_binding(nil, "display-page-" .. page.idx .. "-toggle", function()
         curr_page = k
         process_key_binding(false)
     end, {repeatable=false})