Rename to minimumJavaVersion to keep the name across tooling

Given this field is present in maven-hpi-plugin, update-center, etc.
I think it does not hurt to keep the 'Minimum-Java-Version' name across
various usages to help make it clear.

core/src/main/java/hudson/PluginWrapper.java

@@ -496,13 +496,13 @@ public class PluginWrapper implements Comparable<PluginWrapper>, ModelObject {
     }
 
     /**
-     * Returns the required Java version of this plugin.
-     * @return the required Java version of this plugin.
+     * Returns the minimumJava version of this plugin.
+     * @return the minimum Java version of this plugin.
      *
      * @since TODO
      */
     @Exported
-    public @CheckForNull String getRequiredJavaVersion() {
+    public @CheckForNull String getMinimumJavaVersion() {
         return manifest.getMainAttributes().getValue("Minimum-Java-Version");
     }
 
@@ -757,12 +757,12 @@ public class PluginWrapper implements Comparable<PluginWrapper>, ModelObject {
                 }
             }
 
-            String requiredJavaVersion = getRequiredJavaVersion();
-            if (requiredJavaVersion != null) {
+            String minimumJavaVersion = getMinimumJavaVersion();
+            if (minimumJavaVersion != null) {
                 // TODO replace with calls to Runtime.version() once we're on Java 9+
                 VersionNumber actualVersion = new VersionNumber(System.getProperty("java.specification.version"));
-                if (actualVersion.isOlderThan(new VersionNumber(requiredJavaVersion))) {
-                    versionDependencyError(Messages.PluginWrapper_obsoleteJava(actualVersion.toString(), requiredJavaVersion), actualVersion.toString(), requiredJavaVersion);
+                if (actualVersion.isOlderThan(new VersionNumber(minimumJavaVersion))) {
+                    versionDependencyError(Messages.PluginWrapper_obsoleteJava(actualVersion.toString(), minimumJavaVersion), actualVersion.toString(), minimumJavaVersion);
                 }
             }
         }

core/src/main/java/hudson/model/UpdateSite.java

@@ -973,7 +973,7 @@ public class UpdateSite {
          * @since TODO
          */
         @Exported
-        public final String requiredJava;
+        public final String minimumJavaVersion;
         /**
          * Categories for grouping plugins, taken from labels assigned to wiki page.
          * Can be null.
@@ -1000,6 +1000,7 @@ public class UpdateSite {
             this.title = get(o,"title");
             this.excerpt = get(o,"excerpt");
             this.compatibleSinceVersion = Util.intern(get(o,"compatibleSinceVersion"));
+            this.minimumJavaVersion = Util.intern(get(o, "minimumJavaVersion"));
             this.requiredCore = Util.intern(get(o,"requiredCore"));
             this.categories = o.has("labels") ? internInPlace((String[])o.getJSONArray("labels").toArray(EMPTY_STRING_ARRAY)) : null;
             JSONArray ja = o.getJSONArray("dependencies");
@@ -1134,7 +1135,7 @@ public class UpdateSite {
          */
         public boolean isForNewerJava() {
             try {
-                return requiredJava != null && new VersionNumber(requiredJava).isNewerThan(
+                return minimumJavaVersion != null && new VersionNumber(minimumJavaVersion).isNewerThan(
                         new VersionNumber(System.getProperty("java.specification.version")));
             } catch (NumberFormatException nfe) {
                 return false; // plugin doesn't declare a minimum Java version
@@ -1162,15 +1163,16 @@ public class UpdateSite {
          *
          * @since TODO
          */
-        public VersionNumber getNeededDependenciesRequiredJava() {
+        @CheckForNull
+        public VersionNumber getNeededDependenciesMinimumJavaVersion() {
             VersionNumber versionNumber = null;
             try {
-                versionNumber = requiredJava == null ? null : new VersionNumber(requiredJava);
+                versionNumber = minimumJavaVersion == null ? null : new VersionNumber(minimumJavaVersion);
             } catch (NumberFormatException nfe) {
                 // unable to parse version
             }
             for (Plugin p: getNeededDependencies()) {
-                VersionNumber v = p.getNeededDependenciesRequiredJava();
+                VersionNumber v = p.getNeededDependenciesMinimumJavaVersion();
                 if (v == null) {
                     continue;
                 }

core/src/main/resources/hudson/PluginManager/table.jelly

@@ -108,7 +108,7 @@ THE SOFTWARE.
                         <div class="compatWarning">${%coreWarning(p.requiredCore)}</div>
                       </j:if>
                       <j:if test="${p.isForNewerJava()}">
-                        <div class="compatWarning">${%javaWarning(p.requiredJava)}</div>
+                        <div class="compatWarning">${%javaWarning(p.minimumJavaVersion)}</div>
                       </j:if>
                       <j:if test="${!p.isNeededDependenciesCompatibleWithInstalledVersion(cache)}">
                         <div class="compatWarning">${%depCompatWarning}</div>
@@ -117,7 +117,7 @@ THE SOFTWARE.
                         <div class="compatWarning">${%depCoreWarning(p.getNeededDependenciesRequiredCore().toString())}</div>
                       </j:if>
                       <j:if test="${p.isNeededDependenciesForNewerJava()}">
-                        <div class="compatWarning">${%depJavaWarning(p.getNeededDependenciesRequiredJava().toString())}</div>
+                        <div class="compatWarning">${%depJavaWarning(p.getNeededDependenciesMinimumJavaVersion().toString())}</div>
                       </j:if>
                       <j:if test="${p.hasWarnings()}">
                         <div class="securityWarning">${%securityWarning}