Disable stretchable spaces in multi-row toolbars in wxMSW.

Stretchable separators simply don't work correctly when the space they are
supposed to stretch onto is distributed across several different toolbar rows
or columns, so just disable them for multi-row (or column, for vertical
toolbars) case.

See #13579.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@76104 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Fix background painting of multi-row toolbars in wxMSW.

The item rectangle used wrong vertical coordinates which didn't matter (much?)
for the single row toolbars but was completely wrong for toolbars with more
than one row.

Don't always anchor the rectangle at the window top to avoid this.

See #13579.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@76105 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Fix size calculation for multi-column vertical toolbars in wxMSW.

The width was calculated incorrectly in this case as we simply multiplied the
width of the widest column by their number in this case, but actually each of
them has its own width which needs to be calculated separately.

See #13579.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@76106 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775