Prefer const wherever possible

Summary:
Non-final identifiers make code harder to understand.
This is particularly true for JavaScript where even the *type*
can change as a value gets reassigned later.

This enforces to use `const` whereever possible, but doesn't
"outlaw" `let`. Mixed destructuring is also still allowed.

Used `eslint --fix` to change all existing cases.

Reviewed By: jknoxville

Differential Revision: D16131329

fbshipit-source-id: 2eceaca7c603b71b36e005be5d135e1849f2518d

src/plugins/logs/index.js

@@ -429,7 +429,7 @@ export default class LogTable extends FlipperDevicePlugin<
     if (highlightedRows.size <= 0) {
       // Check if the individual lines in the deeplinkPayload is matched or not.
       const arr = deepLinkPayload.split('\n');
-      for (let msg of arr) {
+      for (const msg of arr) {
         for (let i = rows.length - 1; i >= 0; i--) {
           if (rows[i].filterValue && rows[i].filterValue.includes(msg)) {
             highlightedRows.add(rows[i].key);