On state change, visuals now keep instance data

On state change, visuals now keep instance data

If a visual such as a text visual has instance data (i.e. the text string)
ensure that this is applied following a state change where the visual
is removed and re-added.

Added new method CreateInstancePropertyMap to Visual::Base::Impl,
and methods DoCreateInstancePropertyMap to derived visuals for writing instance data
into. So far, this is for text visual's text property and image visual's desired image
size properties.

TODO: Prevent the visual being re-added if no properties change
(or only animatable properties change) (Whilst taking into account string vs index keys; Property Array vs Vector...

[ Note: this is problematic for gradient visual, which generates a bunch of property arrays whilst Builder has generated Vectors from the equivalent JSON ]

Change-Id: I742c47067fc19fbaeee2f01195f6f00501b16c85
Signed-off-by: David Steele <david.steele@samsung.com>