Ignore `editor.insertSpaces` within strings

<!-- Please search existing issues to avoid creating duplicates. --> Related issues ============== After searching existing issues, I found two open issues, which are closely related, but different. Including links for reference purposes: - #5394 - #46287 <!-- Describe the feature you'd like. --> Feature request =============== Tabs have three uses in code files: 1. Indentation at the beginning of lines - people often prefer to use spaces here 2. Indentation between keys and values or around assignment operators - people often prefer to use spaces here 3. When a literal tab character is required within a string - this should *always* be a tab and never converted to spaces. Currently, the 3rd use-case is difficult/impossible to handle easily in VSCode when `editor.insertSpaces` is set to `true`. The most common place I've encountered this is for RegEx strings in BSD `sed`, which does not support GNU's non-standard `\t` notation for tabs.