Add separated func for deoplete

Deoplete needs `get_complete_position` method and it has a different
signature. It already fetches the input string and attempts to detect
the position with `\k*` regexp patterns.

autoload/ale/completion.vim

@@ -215,6 +215,10 @@ function! ale#completion#GetCompletionPosition() abort
     return l:column - len(l:match) - 1
 endfunction
 
+function! ale#completion#GetCompletionPositionForDeoplete(input) abort
+    return match(a:input, '\k*$')
+endfunction
+
 function! ale#completion#GetCompletionResult() abort
     if exists('b:ale_completion_result')
         return b:ale_completion_result

rplugin/python3/deoplete/sources/ale.py

@@ -27,8 +27,10 @@ class Source(Base):
         self.input_pattern = r'(\.|::|->)\w*$'
 
     # Returns an integer for the start position, as with omnifunc.
-    def get_completion_position(self):
-        return self.vim.call('ale#completion#GetCompletionPosition')
+    def get_complete_position(self, context):
+        return self.vim.call(
+            'ale#completion#GetCompletionPositionForDeoplete', context['input']
+        )
 
     def gather_candidates(self, context):
         # Stop early if ALE can't provide completion data for this buffer.