[Canvas] Fix context elements issue with Element Stats (#32510) (#32540)

## Summary

(closes #32512, closes #32508)

This fixes a bug where element stats was causing a failure due to not every element being an `expressionRenderable` all the time... when first added, `TimeFilter` is `expressionContext` and should be considered `pending`.

This PR also fixes an issue where `resolvedArgs` was not being reset between workpad loads, causing element stats to be compounded.

Co-authored-by: Spencer <email@spalger.com>

x-pack/plugins/canvas/public/components/element_config/element_config.js

@@ -14,7 +14,7 @@ export const ElementConfig = ({ elementStats }) => {
   }
 
   const { total, ready, error } = elementStats;
-  const progress = Math.round(((ready + error) / total) * 100);
+  const progress = total > 0 ? Math.round(((ready + error) / total) * 100) : 100;
 
   return (
     <Fragment>

x-pack/plugins/canvas/public/state/reducers/resolved_args.js

@@ -10,6 +10,7 @@ import { get } from 'lodash';
 import { prepend } from '../../lib/modify_path';
 import * as actions from '../actions/resolved_args';
 import { flushContext, flushContextAfterIndex } from '../actions/elements';
+import { setWorkpad } from '../actions/workpad';
 
 /*
   Resolved args are a way to handle async values. They track the status, value, and error
@@ -130,6 +131,9 @@ export const resolvedArgsReducer = handleActions(
         return state;
       }, transientState);
     },
+    [setWorkpad]: (transientState, {}) => {
+      return set(transientState, 'resolvedArgs', {});
+    },
   },
   {}
 );

x-pack/plugins/canvas/public/state/selectors/workpad.js

@@ -90,6 +90,12 @@ export function getElementCounts(state) {
   Object.keys(resolvedArgs).forEach(resolvedArg => {
     const arg = resolvedArgs[resolvedArg];
     const { expressionRenderable } = arg;
+
+    if (!expressionRenderable) {
+      results.pending++;
+      return;
+    }
+
     const { value, state } = expressionRenderable;
 
     if (value && value.as === 'error') {