TabSheet focus/blur API improvement (#14304)

Simplify the new inner API in the VTabSheet which solves the
focus/blur issue.

The blur and focus events should be linked with the TabSheet
component as a whole. Any click inside the TabSheet should
trigger one single focus and any leave the blur.

Change-Id: I90dd05f056441920a286b6debdc288fb1a9a7e10
TableRowScrolledBottom test upgrade (#14292)

Change-Id: I382a4da5f186239c5791d1e63e9a75ece9039760
UIProviderInitParameter test upgrade (#14292)

Change-Id: I44e7fa4b0d890972d4e6d14c3159aa9db9131c1d
Fixes DragAndDropWrapper does not support choosing a custom component as the drag image (#13836)

Amend : Fixes the comments for the last commit.
Amend 2: Fixes a nullpointer found in a certain test scenario

Change-Id: I72327f5f8ab9e46d88e1ebed8f1db3a7da39d7d8
TreeTablePartialUpdatesPageLength0 test upgrade (#14292)

Change-Id: I8f7717138247c46d7b85f4fab46328d5d118dbef
SortLabelsInTable test upgrade (#14292)

Change-Id: I07d2b0882ea5520f3d7ec30e29d4c42fb9167c9c
Correct error notification behavior on touch devices (#14447)

Change-Id: I610e81aeb3e1f3f124c27e549ba58e9e28cacecf
UIScrollTest test upgrade (#14292)

Change-Id: I5203b69d2f4ad67107ac347bff9b56b6d66c63bd
LabelEmbeddedClickThroughForTable test upgrade (#14292)

Change-Id: Ic9799343357735580976687ee02afb3bec142861
Merge remote-tracking branch 'origin/master' into 7.3