Flatten the published POM

This has mainly 2 advantages for us:

- It removes all the built-time profile/property settings, which could
  make the pom appear more complicated than it is for people looking to
  use MMCoreJ as a dependency. So flatten it to what a dependency
  resolver (Maven/Gradle) will actually see.

- It can allow parameterizing essential values, such as version, by
  templating them and passing them in on the `mvn` command line.

Author: marktsuchida

MMCoreJ_wrap/.gitignore

@@ -1,2 +1,3 @@
 .wraplock
 /target/
+.flattened-pom.xml

MMCoreJ_wrap/pom.xml

@@ -327,6 +327,33 @@ Run the Meson build first:
                     </execution>
                 </executions>
             </plugin>
+
+            <!-- Remove build-specific elements from published POM (probably
+                 less confusing to consumers) -->
+            <plugin>
+                <groupId>org.codehaus.mojo</groupId>
+                <artifactId>flatten-maven-plugin</artifactId>
+                <version>1.7.3</version>
+                <configuration>
+                    <flattenMode>oss</flattenMode>
+                </configuration>
+                <executions>
+                    <execution>
+                        <id>flatten</id>
+                        <phase>process-resources</phase>
+                        <goals>
+                            <goal>flatten</goal>
+                        </goals>
+                    </execution>
+                    <execution>
+                        <id>flatten-clean</id>
+                        <phase>clean</phase>
+                        <goals>
+                            <goal>clean</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
         </plugins>
     </build>