[build] use local opencv docs element-list (#8633)

Fixes opencv cloudflare blocking gradle javadoc builds

docs/build.gradle

@@ -152,7 +152,9 @@ configurations {
 task generateJavaDocs(type: Javadoc) {
     classpath += project(":wpilibj").sourceSets.main.compileClasspath
     options.links("https://docs.oracle.com/en/java/javase/17/docs/api/")
-    options.links("https://docs.opencv.org/4.x/javadoc/")
+    // workaround for opencv site blocking javadoc tool. If the link is changed,
+    // docs/opencv/element-list must be redownloaded
+    options.linksOffline("https://docs.opencv.org/4.10.0/javadoc/", "opencv")
     options.addStringOption("tag", "pre:a:Pre-Condition")
     options.addBooleanOption("Xdoclint/package:" +
             // TODO: v Document these, then remove them from the list

docs/opencv/element-list

@@ -0,0 +1,29 @@
+org.opencv.aruco
+org.opencv.bgsegm
+org.opencv.bioinspired
+org.opencv.calib3d
+org.opencv.core
+org.opencv.dnn
+org.opencv.dnn_superres
+org.opencv.face
+org.opencv.features2d
+org.opencv.highgui
+org.opencv.img_hash
+org.opencv.imgcodecs
+org.opencv.imgproc
+org.opencv.ml
+org.opencv.objdetect
+org.opencv.osgi
+org.opencv.phase_unwrapping
+org.opencv.photo
+org.opencv.plot
+org.opencv.structured_light
+org.opencv.text
+org.opencv.tracking
+org.opencv.utils
+org.opencv.video
+org.opencv.videoio
+org.opencv.wechat_qrcode
+org.opencv.xfeatures2d
+org.opencv.ximgproc
+org.opencv.xphoto