Add the right side of 'code flow' that including code viewer

What does this MR do and why?

Add the right side of 'code flow' that including code viewer

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After
Screen_Recording_2024-06-10_at_15.43.33	Screen_Recording_2024-07-07_at_14.45.03

How to set up and validate locally

1. Upload a GitLab Ultimate license
2. Enable the feature flag (echo "Feature.enable(:vulnerability_code_flow)" | rails c)
3. Clone the code flow project and run his pipeline to display vulnerabilities
4. Navigate to the project => Secure => Vulnerability report => Select the first vulnerability to navigate to the vulnerability details page
5. Apply the following patch to show the new features

Patch

diff --git a/ee/app/assets/javascripts/vulnerabilities/components/vulnerability.vue b/ee/app/assets/javascripts/vulnerabilities/components/vulnerability.vue
index ca4110274476..319e8f7180ae 100644
--- a/ee/app/assets/javascripts/vulnerabilities/components/vulnerability.vue
+++ b/ee/app/assets/javascripts/vulnerabilities/components/vulnerability.vue
@@ -56,6 +56,7 @@ export default {
       },
     },
     showCodeFlowTabs() {
+      return true
       return (
         this.glFeatures.vulnerabilityCodeFlow && !isEmpty(this.vulnerability.details.codeFlows)
       );
diff --git a/ee/app/assets/javascripts/vulnerabilities/components/vulnerability_details.vue b/ee/app/assets/javascripts/vulnerabilities/components/vulnerability_details.vue
index bfbc47e4c041..72fd47398163 100644
--- a/ee/app/assets/javascripts/vulnerabilities/components/vulnerability_details.vue
+++ b/ee/app/assets/javascripts/vulnerabilities/components/vulnerability_details.vue
@@ -221,6 +221,7 @@ export default {
       return this.vulnerability.location?.file && this.vulnerability.location?.startLine;
     },
     showCodeFlowButton() {
+      return true
       return (
         this.glFeatures.vulnerabilityCodeFlow && !isEmpty(this.vulnerability.details.codeFlows)
       );

6. Navigate to code flow tab
7. Verify code viewer appears with highlighted lines
8. Go through the steps using the up and down buttons and verify that the highlight has changed
9. Change theme and verify the highlight colors change

Related to #469653 (closed) and #458062

app/assets/javascripts/vue_shared/components/source_viewer/plugins/language_highlight.js

+import hljsCore from 'highlight.js/lib/core';
+import languageLoader from '~/content_editor/services/highlight_js_language_loader';
+import { ROUGE_TO_HLJS_LANGUAGE_MAP } from '~/vue_shared/components/source_viewer/constants';
+
+const HLJS_ON_AFTER_HIGHLIGHT = 'after:highlight';
+
+const loadLanguage = async (language, hljs) => {
+  const languageDefinition = await languageLoader[language]();
+  hljs.registerLanguage(language, languageDefinition.default);
+};
+
+const loadSubLanguages = async (languageDefinition, hljs) => {
+  // Some files can contain sub-languages (i.e., Svelte); this ensures that sub-languages are also loaded
+  if (!languageDefinition?.contains) return;
+
+  // generate list of languages to load
+  const languages = new Set(
+    languageDefinition.contains
+      .filter((component) => Boolean(component.subLanguage))
+      .map((component) => component.subLanguage),
+  );
+
+  if (languageDefinition.subLanguage) {
+    languages.add(languageDefinition.subLanguage);
+  }
+
+  await Promise.all([...languages].map((language) => loadLanguage(language, hljs)));
+};
+
+// Registers our plugins for Highlight.js
+// Plugin API: https://github.com/highlightjs/highlight.js/blob/main/docs/plugin-api.rst
+const registerPlugins = (hljs, plugins) => {
+  if (!plugins) {
+    return;
+  }
+  for (const plugin of plugins) {
+    hljs.addPlugin({ [HLJS_ON_AFTER_HIGHLIGHT]: plugin });
+  }
+};
+
+const registerLanguage = async (hljs, language) => {
+  await loadLanguage(language, hljs);
+  await loadSubLanguages(hljs.getLanguage(language), hljs);
+};
+
+const initHighlightJs = async (language, plugins) => {
+  const hljs = hljsCore.newInstance();
+
+  registerPlugins(hljs, plugins);
+  await registerLanguage(hljs, language);
+
+  return hljs;
+};
+
+const highlightContent = async (lang, rawContent, plugins) => {
+  const language = ROUGE_TO_HLJS_LANGUAGE_MAP[lang.toLowerCase()];
+  let highlightedContent;
+
+  if (language) {
+    const hljs = await initHighlightJs(language, plugins);
+    highlightedContent = hljs.highlight(rawContent, { language }).value;
+  }
+
+  return highlightedContent;
+};
+
+export { highlightContent };