Reviewed code of #13 (and #9) and tested on Drupal 11.0.1 clean Standard installation with default and custom content types, taxonomy terms, and menu links. The bug experienced is no longer happening. Updating status to RTBC.
Tested patch #2 on clean, Standard installation of Core version 10.2.0, Token 8.x-1.13, and Scheduler 2.0.1. The patch resolves the issue and clears an error message in Status Report: "Token types are not defined but have tokens - $info['types']['taxonomy_term']"
Tested in Drupal 10 on DrupalPod. Module enables and functions as described.
Tested with the latest Drupal Version 9.2.0-dev using MacOS Safari. The patch does resolve the error displaying:
Before patch
Without patch applied, using a placeholder on a date field causes an error
After patch
After applying the patch, using a placehodler on a date field does not cause an error
For this, marking as RTBC.
It's worth noting that Desktop Chrome and Desktop Firefox both override date fields to use the browser's datepicker. To override this behavior, the following guidance is given: http://trac.webkit.org/wiki/Styling%20Form%20Controls#Dateinputtype. Mobile browsers generally use the mobile OS's datepicker.