* [GEOS] Generate debug library names with `d` suffix
Currently geos.lib name is used for both, debug and optimised
GEOS libraries. This leads to situation when:
```
find_library(GEOS_LIBRARY_DEBUG NAMES geos)
find_library(GEOS_LIBRARY_RELEASE NAMES geos)
```
finds the same library for both
```
GEOS_LIBRARY_DEBUG=D:/vcpkg/installed/x64-windows/debug/lib/geos.lib
GEOS_LIBRARY_RELEASE=D:/vcpkg/installed/x64-windows/debug/lib/geos.lib
```
This is minimal patch that works around the problem.
Next, complete fix should be submitted to GEOS upstream,
preferably using exported targets.
* [libspatialite] Add missing geos suffixes in static builds
* Bump GEOS version wherever necessary
* Update download package and checksum.
* Replace download from SVN with official release source package.
* Remove generating of geos_svn_revision.h as unnecessary -
released source package includes the header.
* Explain status of the missing CMake modules.
* Remove CMake option -DBUILD_TESTING as unused.
GEOS is important dependency of GDAL (updated in #1879;
GDAL 2.2.2 can still work with GEOS earlier than 3.6.2).
