[build] Clean up CMake files (#6802)

Explicitly list required components when using FindJava and FindJNI
Consolidate find_package calls for Java, JNI, and OpenCV into the root CMakeLists.txt file
Remove references to main_lib_dest
Install missing generated headers
Flatten some if statements
Use LinkMacOSGUI macro instead of hand rolling it
Stop installing OpenCV libraries and an extra ntcorejni library; OpenCV JAR will still be installed to make it easy to use
Only print platform version on Windows
Prevent GUI modules from being built when wpimath is off, which would otherwise cause a build failure
Simplify build configuration checks
Clean up fieldImages JAR creation
Place built JARs in the same subdir as installed JARs
Remove unnecessary JAR includes
Remove extra directories in target_include_directories
Improve CMake docs

wpilibj/CMakeLists.txt

@@ -2,8 +2,6 @@ project(wpilibj)
 
 # Java bindings
 if(WITH_JAVA)
-    find_package(OpenCV REQUIRED)
-    find_package(Java REQUIRED)
     include(UseJava)
 
     set(OPENCV_JAVA_INSTALL_DIR ${OpenCV_INSTALL_PATH}/share/java/opencv4)
@@ -41,6 +39,7 @@ if(WITH_JAVA)
             wpiunits_jar
             wpiutil_jar
         OUTPUT_NAME wpilibj
+        OUTPUT_DIR ${WPILIB_BINARY_DIR}/${java_lib_dest}
     )
     set_property(TARGET wpilibj_jar PROPERTY FOLDER "java")
 
@@ -51,7 +50,6 @@ if(WITH_JAVA)
 endif()
 
 if(WITH_JAVA_SOURCE)
-    find_package(Java REQUIRED)
     include(UseJava)
     file(
         GLOB WPILIBJ_SOURCES
@@ -95,6 +93,7 @@ if(WITH_JAVA_SOURCE)
         NAMESPACE "edu/wpi/first/wpilibj/smartdashboard" ${WPILIBJ_SMARTDASHBOARD_SOURCES}
         NAMESPACE "edu/wpi/first/wpilibj/util" ${WPILIBJ_UTIL_SOURCES}
         OUTPUT_NAME wpilibj-sources
+        OUTPUT_DIR ${WPILIB_BINARY_DIR}/${java_lib_dest}
     )
 
     get_property(WPILIBJ_SRC_JAR_FILE TARGET wpilibj_src_jar PROPERTY JAR_FILE)