Inspect continuation prompt signature and pass only viable arguments.

[Carreau]

Closes #14273

[tornaria]

While you are at it, maybe remove cli=None from the previous method, and the two lines 46-47 below.

[tornaria]

LGTM, I actually rebuilt ipython with this PR and tried running sagemath to make sure.

My suggestion above in patch form:

--- a/docs/source/config/details.rst
+++ b/docs/source/config/details.rst
@@ -33,7 +33,7 @@ which defines the defaults. The required interface is like this:
    Prompt style definition. *shell* is a reference to the
    :class:`~.TerminalInteractiveShell` instance.
 
-   .. method:: in_prompt_tokens(cli=None)
+   .. method:: in_prompt_tokens()
                continuation_prompt_tokens(self, width=None)
                rewrite_prompt_tokens()
                out_prompt_tokens()
@@ -43,9 +43,6 @@ which defines the defaults. The required interface is like this:
       For continuation prompts, *width* is an integer representing the width of
       the prompt area in terminal columns.
 
-      *cli*, where used, is the prompt_toolkit ``CommandLineInterface`` instance.
-      This is mainly for compatibility with the API prompt_toolkit expects.
-
 Here is an example Prompt class that will show the current working directory
 in the input prompt:
 
@@ -55,7 +52,7 @@ in the input prompt:
     import os
 
     class MyPrompt(Prompts):
-         def in_prompt_tokens(self, cli=None):
+         def in_prompt_tokens(self):
              return [(Token, os.getcwd()),
                      (Token.Prompt, ' >>>')]
 

Maybe you also want to patch out the examples:

--- a/examples/Embedding/embed_class_long.py
+++ b/examples/Embedding/embed_class_long.py
@@ -21,7 +21,7 @@
 
 class CustomPrompt(Prompts):
 
-    def in_prompt_tokens(self, cli=None):
+    def in_prompt_tokens(self):
 
        return [
             (Token.Prompt, 'In <'),
--- a/examples/utils/cwd_prompt.py
+++ b/examples/utils/cwd_prompt.py
@@ -6,7 +6,7 @@
 
 class MyPrompt(Prompts):
 
-     def in_prompt_tokens(self, cli=None):
+     def in_prompt_tokens(self):
          return [(Token, os.getcwd()),
                  (Token.Prompt, '>>>')]