Fix wrong resulting string length in UTF-16 to wchar_t conversion.

Don't optimize the returned length for surrogate-less case, this does save a
pass of the string but at the price of returning a wrong result, which is not
worth it, just compute the really required length exactly.

Closes #16298.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76622 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Correct handling of the characters outside of the BMP in wxSTC.

The code mapping positions for the units of the UTF-13/32 string used by
wxWidgets to positions for the units of the UTF-8 string used by Scintilla
didn't work correctly for the characters outside of the BMP, i.e. Unicode code
points >= 0x10000.

See #15621.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76623 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Fix cancelling choice of custom colour in wxPropertyGrid.

When using wxPGEditor_Choice colour property, cancelling the choice of the
custom colour reset the previously selected custom colour.

Fix this by correcting the test for the custom colour which didn't work
before.

Closes #15542.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76624 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Update the instructions about adding a new wxUSE_FOO symbol.

Mention wx/chkconf.h.

Provide specific instructions for MSW-specific options.

Don't tell people to update wx/univ/setup.h (it is auto-generated) nor
setup.h_vms (it is manually updated by the OpenVMS maintainer).

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76625 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775