The current error reporting first deletes all markers and recreates
them. This modifies the workspace's element tree and thereby invalidates
the cached delta in BuildManager even if no markers actually change.

This change introduces IncrementalErrorReporter which collects marker
attributes for reported problems and tries to find an existing marker
with equal attributes. If it finds one, the marker is kept and no
changes to the element tree are necessary.

Change-Id: I8135d04229d56b9c0e5ce3fbde6ed8e7df24d2fa
Signed-off-by: Julian Honnen <julian.honnen@vector.com>
Signed-off-by: Andrey Loskutov <loskutov@gmx.de>