emulators/es-de: Simplify port

Remove unnecessary localbase from USES.
Promote unbundled utf8cpp include path to CMakeLists.txt instead of replacing
C include directive in ${WRKSRC}/es-core/utils/StringUtil.h.
Use CMake's modules for finding unbundled RapidJSON and rlottie package.
This allows to remove the INCLUDE_DIRS for both libraries (CMake already does
the right thing when using find_package).
Replace rlottie_LINK_LIBRARIES with the more proper rlottie_LIBRARIES.

PR: 282698
Approved by: submitter is maintainer