[Also for ICU4j]
Add syntax that permits MessageFormat to do monospace column display.
Thoughts:
Have a syntax character (X) that does not interfere with MessageFormat. Add at
the end of the message format, after the X, a list of tab stops.
13L means left tabstop at position 13
19R means right tabstop at position 19
19D means decimal tabstop at position 19
19C means center tabstop at position 19
Positions must be in ascending order. Tabstops are separated by spaces.
Tabs from the textare transformed into spaces to make the above constraints
work. [With normal handling for overflow.] Decimal tabs can make use of a number
format at the position, if there is one. Otherwise they use the MessageFormat's
locale to get the decimal point.
