Do not force md download always (#11908)

My proposal, go back to original behaviour with a twist:
* discover via project (if present) -- but added slight heuristics to try to prioritize plugins that have prefix in A (ie "spotless" -> "spotless-maven-plugin"), and then try all the remainers if not found
* discover via G level metadata

Rationale: original change was IMHO wrong: not only it allowed "takeover" of prefix, user was not able to do anything about it. The original code (where this PR goes back to) was done like this on purpose: the user input (POM) is mandatory, so if user defines a plugin, and it has given prefix, that must be used, whatever any remote repository G level metadata says. Only if there is no user instruction, go for prefix discovery via metadata.

Code uses `Set` and gets rid of the possible double resolution of same plugin, as they may coexist (usually is) in project/build/plugins and project/build/pluginManagement/plugins.

Fixes #11905

Author: cstamas

maven-core/src/main/java/org/apache/maven/plugin/prefix/internal/DefaultPluginPrefixResolver.java

@@ -24,8 +24,10 @@
 
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.Collection;
 import java.util.Collections;
 import java.util.LinkedHashMap;
+import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -105,16 +107,20 @@ public PluginPrefixResult resolve(PluginPrefixRequest request) throws NoPluginFo
                         LinkedHashMap::new,
                         Collectors.mapping(Plugin::getArtifactId, Collectors.toSet())));
         request.getPluginGroups().forEach(g -> candidates.put(g, null));
-        PluginPrefixResult result = resolveFromRepository(request, candidates);
-
-        // If we haven't been able to resolve the plugin from the repository,
-        // as a last resort, we go through all declared plugins, load them
+        PluginPrefixResult result = null;
+        // First, we go through all declared plugins, load them
         // one by one, and try to find a matching prefix.
-        if (result == null && build != null) {
-            result = resolveFromProject(request, build.getPlugins());
-            if (result == null && management != null) {
-                result = resolveFromProject(request, management.getPlugins());
-            }
+        if (build != null) {
+            result = resolveFromProject(
+                    request,
+                    build.getPlugins(),
+                    management != null ? management.getPlugins() : Collections.emptyList());
+        }
+
+        // Second, we go use G level metadata to discover prefix
+        // This order allows user managed clashing prefixes (they can declare them in POM)
+        if (result == null) {
+            result = resolveFromRepository(request, candidates);
         }
 
         if (result == null) {
@@ -132,7 +138,30 @@ public PluginPrefixResult resolve(PluginPrefixRequest request) throws NoPluginFo
         return result;
     }
 
-    private PluginPrefixResult resolveFromProject(PluginPrefixRequest request, List<Plugin> plugins) {
+    private PluginPrefixResult resolveFromProject(
+            PluginPrefixRequest request, List<Plugin> plugins, List<Plugin> pluginMgmt) {
+        if (plugins.isEmpty() && pluginMgmt.isEmpty()) {
+            return null;
+        }
+        PluginPrefixResult result = null;
+        // try optimistically; first if A contains prefix?
+        Set<Plugin> candidates = new LinkedHashSet<>();
+        Stream.concat(plugins.stream(), pluginMgmt.stream())
+                .filter(p -> p.getArtifactId().contains(request.getPrefix()))
+                .forEach(candidates::add);
+        if (!candidates.isEmpty()) {
+            result = doResolveFromProject(request, candidates);
+        }
+        // if no luck; try the rest
+        if (result == null) {
+            Set<Plugin> remainder = new LinkedHashSet<>(plugins);
+            remainder.removeAll(candidates);
+            result = doResolveFromProject(request, remainder);
+        }
+        return result;
+    }
+
+    private PluginPrefixResult doResolveFromProject(PluginPrefixRequest request, Collection<Plugin> plugins) {
         for (Plugin plugin : plugins) {
             try {
                 PluginDescriptor pluginDescriptor =