Use PASE perl to run manual generation scripts.
As PASE perl is not aware of all possible input file encoding, convert
all files to UTF-8 upon build start (this might be lengthy).
OS/400 terminal emulation may only offer 76 columns, thus a new -c
parameter has been added to the managen program, defining the allowed
width.
If perl is not available, omit generation and disable online manual.
Closes#14289
