Enable the ESLint prefer-const rule globally (PR 11450 follow-up)

Please find additional details about the ESLint rule at https://eslint.org/docs/rules/prefer-const

With the recent introduction of Prettier this sort of mass enabling of ESLint rules becomes a lot easier, since the code will be automatically reformatted as necessary to account for e.g. changed line lengths.

Note that this patch is generated automatically, by using the ESLint `--fix` argument, and will thus require some additional clean-up (which is done separately).

src/display/api.js

@@ -1828,7 +1828,9 @@ const PDFWorker = (function PDFWorkerClosure() {
           });
 
           const sendTest = () => {
-            let testObj = new Uint8Array([this.postMessageTransfers ? 255 : 0]);
+            const testObj = new Uint8Array([
+              this.postMessageTransfers ? 255 : 0,
+            ]);
             // Some versions of Opera throw a DATA_CLONE_ERR on serializing the
             // typed array. Also, checking if we can use transfers.
             try {