jsoncpp: also provide JsonCpp::JsonCpp target

[SpaceIm]

target added in upstream config file in 1.9.5 (open-source-parsers/jsoncpp#1271)

---

• I've read the guidelines for contributing.
• I've followed the PEP8 style guides for Python code in the recipes.
• I've used the latest Conan client version.
• I've tried at least one configuration locally with the conan-center hook activated.

[conan-center-bot]

All green in build 1 (255dcae6614ed4903eecc47f99a5eccc1945ec4c):

• jsoncpp/1.9.5@:
  All packages built successfully! (All logs)

• jsoncpp/1.9.2@:
  All packages built successfully! (All logs)

• jsoncpp/1.9.3@:
  All packages built successfully! (All logs)

• jsoncpp/1.9.4@:
  All packages built successfully! (All logs)

• jsoncpp/1.9.1@:
  All packages built successfully! (All logs)

• jsoncpp/1.8.3@:
  All packages built successfully! (All logs)

[github-actions]

Hooks produced the following warnings for commit 255dcae

jsoncpp/1.9.5

post_package(): WARN: [MISSING SYSTEM LIBS (KB-H043)] Library './lib/libjsoncpp.so' links to system library 'm' but it is not in cpp_info.system_libs.

jsoncpp/1.9.2

post_package(): WARN: [MISSING SYSTEM LIBS (KB-H043)] Library './lib/libjsoncpp.so' links to system library 'm' but it is not in cpp_info.system_libs.

jsoncpp/1.9.3

post_package(): WARN: [MISSING SYSTEM LIBS (KB-H043)] Library './lib/libjsoncpp.so' links to system library 'm' but it is not in cpp_info.system_libs.

jsoncpp/1.9.4

post_package(): WARN: [MISSING SYSTEM LIBS (KB-H043)] Library './lib/libjsoncpp.so' links to system library 'm' but it is not in cpp_info.system_libs.

jsoncpp/1.9.1

post_package(): WARN: [MISSING SYSTEM LIBS (KB-H043)] Library './lib/libjsoncpp.so' links to system library 'm' but it is not in cpp_info.system_libs.

jsoncpp/1.8.3

post_package(): WARN: [MISSING SYSTEM LIBS (KB-H043)] Library './lib/libjsoncpp.so' links to system library 'm' but it is not in cpp_info.system_libs.