[eclipse-pmc] API Addition To Move 'Spaces For Tabs' to Platform Text

[Daniel Megert <daniel_megert@xxxxxxxxxx>]

In order to provide 'Spaces for Tabs' support for all textual editors I
need to push down the relevant code (converter, preference constants)  from
JDT Text down to Platform Text and make parts of it API. For details see
patch attached to the bug report.


GOALS/BENEFITS:
- 'Insert spaces for tabs' in all textual editors (Ant and possibly other
editor provider can remove a wad of code)
- provide feature as advertised on 3.3. plan


CORRESPONDING BUG:
- [typing][preferences] Move "tabs to spaces" function from JavaEditor to
TextEditor
      https://bugs.eclipse.org/bugs/show_bug.cgi?id=82296


RISKS:
Clients that already provide such a preference (e.g. Ant) will either have
to remove their code or ignore the general text preference. This will be
reflected in the migration guide.


PERFORMANCE IMPACTS:
None.


Dani