js: custom-init: use ~~/init.js instead of ~~/.init.js (dot)

mpv doesn't have other dot files in its config dir, and it also
shouldn't be "invisible".

The new name ~~/init.js now replaces ~~/.init.js

While mpv usually deprecates things before outright removing them,
in this case the old (dot) name is replaced without deprecation:
- It's a bad idea to execute hidden scripts, even if at a config dir,
  and we don't want to do that for the next release cycle too.
- We warn if the old (dot) name exists and the new name doesn't,
  which should be reasonably visible for affected users.
- It's likely niche enough to not cause too much pain.

If for some reason both names are needed, e.g. when using also an old
mpv versions, then the old name could be symlinked to the new one, or
simply have one line: `require("~~/init")` to load the new name, while
a new mpv version will load (only) the new name without warning.

DOCS/interface-changes.rst

@@ -47,6 +47,8 @@ Interface changes
       bindings during start-up (default: yes).
     - add ``track-list/N/image`` sub-property
     - remove `--opengl-restrict` option
+    - js custom-init: use filename ~~/init.js instead of ~~/.init.js (dot)
+
  --- mpv 0.33.0 ---
     - add `--d3d11-exclusive-fs` flag to enable D3D11 exclusive fullscreen mode
       when the player enters fullscreen.

DOCS/man/javascript.rst

@@ -336,7 +336,7 @@ Custom initialization
 ---------------------
 
 After mpv initializes the JavaScript environment for a script but before it
-loads the script - it tries to run the file ``.init.js`` at the root of the mpv
+loads the script - it tries to run the file ``init.js`` at the root of the mpv
 configuration directory. Code at this file can update the environment further
 for all scripts. E.g. if it contains ``mp.module_paths.push("/foo")`` then
 ``require`` at all scripts will search global module id's also at ``/foo``
@@ -345,6 +345,8 @@ paths - like ``<script-dir>/modules`` for scripts which load from a directory).
 
 The custom-init file is ignored if mpv is invoked with ``--no-config``.
 
+Before mpv 0.34, the file name was ``.init.js`` (with dot) at the same dir.
+
 The event loop
 --------------
 

player/javascript/defaults.js

@@ -769,12 +769,16 @@ g.mp_event_loop = function mp_event_loop() {
     } while (mp.keep_running);
 };
 
-})(this)
 
 // let the user extend us, e.g. by adding items to mp.module_paths
-// (unlike e.g. read_file, file_info doesn't expand meta-paths)
-if (mp.get_property_bool("config") &&  // --no-config disables custom init
-    mp.utils.file_info(mp.utils.get_user_path("~~/.init.js")))
-{
-    require("~~/.init");
+if (mp.get_property_bool("config")) {  // --no-config disables custom init
+    // file_info doesn't expand meta-paths (other file functions do)
+    var file_info = mp.utils.file_info, user_path = mp.utils.get_user_path;
+
+    if (file_info(user_path("~~/init.js")))
+        require("~~/init");
+    else if (file_info(user_path("~~/.init.js")))
+        mp.msg.warn("Config file ~~/.init.js is ignored. Use ~~/init.js");
 }
+
+})(this)