Refactor sastReportsInInlineDiff handling

What does this MR do and why?

This MR is an iteration on solving: #417007 (closed)

It refactors the handling of the sast_reports_in_inline_diff flag (rollout Issue) on the client side.

Why would we want to do that? The required UI changes described in the Issue above make it necessary that the findings-detail information will be living as a direct child from the gutter icon in the future. Currently the detail information are living on the same level next to the findings-gutter icon.

• This MR refactors the SAST inline findings out of the expanded-view, since they will be shown in a dropdown (to be added in follow-up MR)
• adds a new flag-toggle in the diff_row component so that we can make the switch between the two UX components easily and only have a single source of truth.
• This makes it easy to remove the expanded section completely once the flag will be removed

Adding the new Findings UI will be done in a separate MR to keep the size of the MR's at a manageable level.

Screenshots or screen recordings

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

with sast_reports_in_inline_diff false

no visual changes

Before	After
MR1_flag_off_before	MR1_flag_off_after

with sast_reports_in_inline_diff true

no expanded section, popover will be introduced in follow-up MR

Before	After
MR1_flag_on_before	MR1_flag_on_after

How to set up and validate locally

1. Clone this repo: https://gitlab.com/jannik_lehmann/sast-inline-findings-example
2. Recreate this MR: jannik_lehmann/sast-inline-findings-example!1 (merged)
3. Let the Pipeline finish and see the Security findings in action
4. Clone this repo: https://gitlab.com/jannik_lehmann/code-quality-test
5. Recreate this MR: jannik_lehmann/code-quality-test!4 (diffs)
6. Let the pipeline finish and see that the CodeQuality Findings are still working.
7. Enable this flag: sast_reports_in_inline_diff
8. Apply the patch below
9. Go to recreated MR, see CQ and (mocked)-Security finding on same line

diff --git a/app/assets/javascripts/diffs/index.js b/app/assets/javascripts/diffs/index.js
index b9cf26827f26..f487574edcf9 100644
--- a/app/assets/javascripts/diffs/index.js
+++ b/app/assets/javascripts/diffs/index.js
@@ -32,7 +32,8 @@ export default function initDiffsApp(store = notesStore) {
       return {
         endpointCoverage: dataset.endpointCoverage || '',
         endpointCodequality: dataset.endpointCodequality || '',
-        endpointSast: dataset.endpointSast || '',
+        // endpointSast: dataset.endpointSast || '',
+        endpointSast: 'mockedEndpoint',
         helpPagePath: dataset.helpPagePath,
         currentUser: JSON.parse(dataset.currentUserData) || {},
         changesEmptyStateIllustration: dataset.changesEmptyStateIllustration,
diff --git a/ee/app/assets/javascripts/diffs/store/actions.js b/ee/app/assets/javascripts/diffs/store/actions.js
index 3c91c1fc3482..b70aac7b3976 100644
--- a/ee/app/assets/javascripts/diffs/store/actions.js
+++ b/ee/app/assets/javascripts/diffs/store/actions.js
@@ -100,6 +100,23 @@ export const setGenerateTestFilePath = ({ commit }, path) =>
   commit(types.SET_GENERATE_TEST_FILE_PATH, path);
 
 export const fetchSast = ({ commit, state, dispatch }) => {
+  commit(types.SET_SAST_DATA, {
+    added: [
+      {
+        severity: "medium",
+        description:
+          "Markup escaping disabled. This can be used with some template engines to escape\ndisabling of HTML entities, which can lead to XSS attacks.\n",
+        location: {
+          file: "noise.rb",
+          start_line: 7,
+        },
+      },
+    ],
+    fixed: [],
+  });
+
+  return;
+
   let retryCount = 0;
   sastPoll = new Poll({
     resource: {

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.