Check for dot being available when building HTML documentation.

This helps with ensuring that the generated CHM always has the inheritance
diagrams as by default Doxygen creates it successfully even if dot is not
found -- but without any graphs.

Closes #15620.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@75095 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Fix wxSpinButton default width under GTK+ 3.

The default GTK+2 width is so small as to make the control unusable under
GTK+3, so use larger (but still hardcoded) width there.

Closes #15619.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@75096 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Fix MeasureWidths() in wxSTC in non-Unicode build.

Integer values must be converted to floats instead of just using memcpy().

Closes #15617.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@75097 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775