Add some defaults to tkinter.filedialog (python#13345)

Partially fixes: python#11482

Source of fixes based on the @Akuli comment: python#11482 (comment)

stdlib/tkinter/filedialog.pyi

@@ -80,8 +80,8 @@ class Directory(commondialog.Dialog):
 # TODO: command kwarg available on macos
 def asksaveasfilename(
     *,
-    confirmoverwrite: bool | None = ...,
-    defaultextension: str | None = ...,
+    confirmoverwrite: bool | None = True,
+    defaultextension: str | None = "",
     filetypes: Iterable[tuple[str, str | list[str] | tuple[str, ...]]] | None = ...,
     initialdir: StrOrBytesPath | None = ...,
     initialfile: StrOrBytesPath | None = ...,
@@ -91,7 +91,7 @@ def asksaveasfilename(
 ) -> str: ...  # can be empty string
 def askopenfilename(
     *,
-    defaultextension: str | None = ...,
+    defaultextension: str | None = "",
     filetypes: Iterable[tuple[str, str | list[str] | tuple[str, ...]]] | None = ...,
     initialdir: StrOrBytesPath | None = ...,
     initialfile: StrOrBytesPath | None = ...,
@@ -101,7 +101,7 @@ def askopenfilename(
 ) -> str: ...  # can be empty string
 def askopenfilenames(
     *,
-    defaultextension: str | None = ...,
+    defaultextension: str | None = "",
     filetypes: Iterable[tuple[str, str | list[str] | tuple[str, ...]]] | None = ...,
     initialdir: StrOrBytesPath | None = ...,
     initialfile: StrOrBytesPath | None = ...,
@@ -110,15 +110,15 @@ def askopenfilenames(
     typevariable: StringVar | str | None = ...,
 ) -> Literal[""] | tuple[str, ...]: ...
 def askdirectory(
-    *, initialdir: StrOrBytesPath | None = ..., mustexist: bool | None = ..., parent: Misc | None = ..., title: str | None = ...
+    *, initialdir: StrOrBytesPath | None = ..., mustexist: bool | None = False, parent: Misc | None = ..., title: str | None = ...
 ) -> str: ...  # can be empty string
 
 # TODO: If someone actually uses these, overload to have the actual return type of open(..., mode)
 def asksaveasfile(
     mode: str = "w",
     *,
-    confirmoverwrite: bool | None = ...,
-    defaultextension: str | None = ...,
+    confirmoverwrite: bool | None = True,
+    defaultextension: str | None = "",
     filetypes: Iterable[tuple[str, str | list[str] | tuple[str, ...]]] | None = ...,
     initialdir: StrOrBytesPath | None = ...,
     initialfile: StrOrBytesPath | None = ...,
@@ -129,7 +129,7 @@ def asksaveasfile(
 def askopenfile(
     mode: str = "r",
     *,
-    defaultextension: str | None = ...,
+    defaultextension: str | None = "",
     filetypes: Iterable[tuple[str, str | list[str] | tuple[str, ...]]] | None = ...,
     initialdir: StrOrBytesPath | None = ...,
     initialfile: StrOrBytesPath | None = ...,
@@ -140,7 +140,7 @@ def askopenfile(
 def askopenfiles(
     mode: str = "r",
     *,
-    defaultextension: str | None = ...,
+    defaultextension: str | None = "",
     filetypes: Iterable[tuple[str, str | list[str] | tuple[str, ...]]] | None = ...,
     initialdir: StrOrBytesPath | None = ...,
     initialfile: StrOrBytesPath | None = ...,