How to check for hard-coded values in Excel formulas?

Here is a common problem. Imagine you are looking at a complex spreadsheet, aptly titled "Corporate Strategy 2020.xlsx" which has 17 tabs, umpteen formulas and unclean structure. Whoever designed it was in insane hurry.

The workbook has formulas like this:

So how do you go about detecting all cells containing formulas with hard-coded values?

Alas, the usual methods fail. To solve this problem, let's build 'Detect hard-coded formulas' feature for Excel.