Find and replace text across a single range, one sheet, or every sheet in a Google Spreadsheet, with optional case matching and regex.

Documented steps

1. POST https://sheets.googleapis.com/v4/spreadsheets/{spreadsheetId}:batchUpdate using OAuth scope https://www.googleapis.com/auth/spreadsheets.
2. Add requests[0].findReplace.find = the search string and requests[0].findReplace.replacement = the replacement string.
3. Set exactly one scope field: findReplace.range = GridRange (a specific range), findReplace.sheetId = integer (an entire sheet), or findReplace.allSheets = true (every sheet in the spreadsheet).
4. Optionally set matchCase (case-sensitive match), matchEntireCell (cell value must equal find exactly), and includeFormulas (search formula text rather than just displayed values).
5. Set searchByRegex = true to treat find as a regular expression; per the docs, find and replacement follow Java regex rules and the replacement string may refer to capturing groups — e.g. find "o.* (.*)" with replacement "$1 Rocks" turns "Google Sheets" into "GSheets Rocks".
6. The findReplace reply in replies[] reports counts of values/formulas/rows/sheets changed — check it to confirm the replacement actually matched something.
7. Docs: https://developers.google.com/workspace/sheets/api/reference/rest/v4/spreadsheets/request | https://developers.google.com/workspace/sheets/api/limits