Switch to running the actual install_gadget.py

This re-uses the OutputView code to run the installer script. Refactor
to remove connection from the base OutputView (and other places, it
wasn't used - only used after ConnectionUp).

This also consolidates the stdout and stderr buffers for running jobs.
The distinction was always arbitrary and probably an error, based on the
fact that they were separate in the APIs not based on usability.

python3/vimspector/utils.py

@@ -72,20 +72,18 @@ def OpenFileInCurrentWindow( file_name ):
 
 
 def SetUpCommandBuffer( cmd, name, api_prefix ):
-  bufs = vim.eval(
-    'vimspector#internal#{}job#StartCommandWithLog( {}, "{}" )'.format(
-      api_prefix,
-      json.dumps( cmd ),
-      name ) )
+  buf = Call( f'vimspector#internal#{api_prefix}job#StartCommandWithLog',
+              cmd,
+              name )
 
-  if bufs is None:
+  if buf is None:
     raise RuntimeError( "Unable to start job {}: {}".format( cmd, name ) )
-  elif not all( int( b ) > 0 for b in bufs ):
+  elif int( buf ) <= 0:
     raise RuntimeError( "Unable to get all streams for job {}: {}".format(
       name,
       cmd ) )
 
-  return [ vim.buffers[ int( b ) ] for b in bufs ]
+  return vim.buffers[ int( buf ) ]
 
 
 def CleanUpCommand( name, api_prefix ):
@@ -558,7 +556,6 @@ def Call( vimscript_function, *args ):
     call += 'g:' + arg_name
 
   call += ')'
-  _logger.debug( 'Calling: {}'.format( call ) )
   return vim.eval( call )
 
 
@@ -633,16 +630,26 @@ def HideSplash( api_prefix, splash ):
   return None
 
 
+def GetVimString( vim_dict, name, default=None ):
+
+  # FIXME: use 'encoding' ?
+  try:
+    value = vim_dict[ name ]
+  except KeyError:
+    return default
+
+  if isinstance( value, bytes ):
+    return value.decode( 'utf-8' )
+  return value
+
+
 def GetVimspectorBase():
-  base = vim.vars.get( 'vimspector_base_dir' )
-  if base is None:
-    return os.path.abspath( os.path.join( os.path.dirname( __file__ ),
-                                          '..',
-                                          '..' ) )
-  elif isinstance( base, bytes ):
-    return base.decode( 'utf-8' )
-  else:
-    return base
+  return GetVimString( vim.vars,
+                       'vimspector_base_dir',
+                       os.path.abspath(
+                         os.path.join( os.path.dirname( __file__ ),
+                                       '..',
+                                       '..' ) ) )
 
 
 def GetUnusedLocalPort():
@@ -655,5 +662,7 @@ def GetUnusedLocalPort():
   return port
 
 
-def WindowID( window, tab ):
+def WindowID( window, tab=None ):
+  if tab is None:
+    tab = window.tabpage
   return int( Call( 'win_getid', window.number, tab.number ) )