[z/OS] treat text files as text files so auto-conversion is done (#90128)

To support auto-conversion on z/OS text files need to be opened as text files. These changes will fix a number of LIT failures due to text files not being converted to the internal code page.

update a number of tools so they open the text files as text files
add support in the cat.py to open a text file as a text file (Windows will continue to treat all files as binary so new lines are handled correctly)
add env var definitions to enable auto-conversion in the lit config file.