Custom "Column title" is not working in Pulses for joined tables

[flamber]

Describe the bug
Creating a question with joins and modifying the column titles, then only the columns of the base table is displayed correctly in Pulses, whereas columns for (implicit/explicit) joined tables will show a combination of the normalized table name and column name from Data Model.
The base table's column titles was handled in #11655.

Possible workarounds is to change the column name in Admin > Data Model, or create a SQL question with corrected column names and use that. This might not be possible in every situation.

To Reproduce

1. Custom question > Sample Dataset > Orders - only select ID column
2. Join Products - only select Category column
   
3. Visualization Settings > add one column from People table
4. Modify the "Column title" for each of the three visible columns
   
5. Save question and ➕ > New pulse > add the question, which then only shows custom column title for the base table's columns
   

Information about your Metabase Installation:
Tested 0.37.8 thru 0.39.3, but it's likely been like this forever.

Additional context
Very related to #3735 (and a bit to #11936)

[markbastian]

Related to #18572?