Convert discover_page to ts, remove redundunt methods (#59312)

* convert discover_page to ts

* remove deuplicated methods, improve tests

Author: dmlemeshko

src/legacy/core_plugins/kibana/public/discover/np_ready/angular/discover.html

@@ -23,7 +23,7 @@ <h1 class="euiScreenReaderOnly">{{screenTitle}}</h1>
 
   <main class="container-fluid">
     <div class="row">
-      <div class="col-md-2 sidebar-container collapsible-sidebar" id="discover-sidebar">
+      <div class="col-md-2 sidebar-container collapsible-sidebar" id="discover-sidebar" data-test-subj="discover-sidebar">
         <div class="dscFieldChooser">
           <disc-field-chooser
             columns="state.columns"

test/functional/apps/discover/_discover_histogram.js

@@ -23,6 +23,7 @@ export default function({ getService, getPageObjects }) {
   const log = getService('log');
   const esArchiver = getService('esArchiver');
   const browser = getService('browser');
+  const elasticChart = getService('elasticChart');
   const kibanaServer = getService('kibanaServer');
   const PageObjects = getPageObjects(['settings', 'common', 'discover', 'header', 'timePicker']);
   const defaultSettings = {
@@ -64,7 +65,7 @@ export default function({ getService, getPageObjects }) {
       await PageObjects.timePicker.setAbsoluteRange(fromTime, toTime);
       await PageObjects.discover.setChartInterval('Monthly');
       await PageObjects.header.waitUntilLoadingHasFinished();
-      const chartCanvasExist = await PageObjects.discover.chartCanvasExist();
+      const chartCanvasExist = await elasticChart.canvasExists();
       expect(chartCanvasExist).to.be(true);
     });
     it('should visualize weekly data with within DST changes', async () => {
@@ -74,7 +75,7 @@ export default function({ getService, getPageObjects }) {
       await PageObjects.timePicker.setAbsoluteRange(fromTime, toTime);
       await PageObjects.discover.setChartInterval('Weekly');
       await PageObjects.header.waitUntilLoadingHasFinished();
-      const chartCanvasExist = await PageObjects.discover.chartCanvasExist();
+      const chartCanvasExist = await elasticChart.canvasExists();
       expect(chartCanvasExist).to.be(true);
     });
     it('should visualize monthly data with different years Scaled to 30d', async () => {
@@ -84,7 +85,7 @@ export default function({ getService, getPageObjects }) {
       await PageObjects.timePicker.setAbsoluteRange(fromTime, toTime);
       await PageObjects.discover.setChartInterval('Daily');
       await PageObjects.header.waitUntilLoadingHasFinished();
-      const chartCanvasExist = await PageObjects.discover.chartCanvasExist();
+      const chartCanvasExist = await elasticChart.canvasExists();
       expect(chartCanvasExist).to.be(true);
     });
   });

test/functional/apps/discover/_source_filters.js

@@ -49,7 +49,6 @@ export default function({ getService, getPageObjects }) {
     });
 
     it('should not get the field referer', async function() {
-      //let  fieldNames;
       const fieldNames = await PageObjects.discover.getAllFieldNames();
       expect(fieldNames).to.not.contain('referer');
       const relatedContentFields = fieldNames.filter(