Include LICENSE in the generated jar under META-INF.

Fixes #6468

I'd looked at [how Guice does this](https://github.com/google/guice/blob/40a5bcfab5cfe45c3b6c5ffc9309b310df82775b/pom.xml#L255-L273), which pulls the Apache license from a remote server (and also generates additional `DEPENDENCIES` and `NOTICE` files). But I figured it was simplest to just point `maven-resources-plugin` at our local `LICENSE` file: `maven-resources-plugin` can work with any license, whereas I'm not sure if Guice's `apache-jar-resource-bundle` approach can. Plus, I want to figure `maven-resources-plugin` out, anyway, for [Proguard purposes](#2117).

Conveniently, I'm pretty confident that our existing `resources` configuration isn't necessary: Maybe it was years ago, but nowadays, we have no results for `find */src android/*/src -type f -not -name '*.java'` (except under `guava-gwt`, which overrides `resources` and which I verified builds an identical jar after this change).

RELNOTES=n/a
PiperOrigin-RevId: 530360631

android/pom.xml

@@ -71,11 +71,11 @@
     <testSourceDirectory>test</testSourceDirectory>
     <resources>
       <resource>
-        <directory>src</directory>
-        <excludes>
-          <exclude>**/*.java</exclude>
-          <exclude>**/*.sw*</exclude>
-        </excludes>
+        <directory>../..</directory>
+        <includes>
+          <include>LICENSE</include>
+        </includes>
+        <targetPath>META-INF</targetPath>
       </resource>
     </resources>
     <testResources>

pom.xml

@@ -72,11 +72,11 @@
     <testSourceDirectory>test</testSourceDirectory>
     <resources>
       <resource>
-        <directory>src</directory>
-        <excludes>
-          <exclude>**/*.java</exclude>
-          <exclude>**/*.sw*</exclude>
-        </excludes>
+        <directory>..</directory>
+        <includes>
+          <include>LICENSE</include>
+        </includes>
+        <targetPath>META-INF</targetPath>
       </resource>
     </resources>
     <testResources>