Fix a bug in core_settings.gradle with relative paths

I think this has been broken since 617267b (which was trying to fix
the same problem).

This change initializes `rootDir` to always be the current project (i.e. ExoPlayer)
directory. From the [Gradle docs](https://docs.gradle.org/current/userguide/working_with_files.html#sec:single_file_paths):
> What happens in the case of multi-project builds? The file() method
> will always turn relative paths into paths that are relative to the
> current project directory, which may be a child project.

We can also then remove exoplayerRoot completely and simplify the local
dependency instructions.

* #minor-release
* #exofixit
* Issue: #9403

PiperOrigin-RevId: 395478121

README.md

@@ -115,9 +115,8 @@ Next, add the following to your project's `settings.gradle` file, replacing
 `path/to/exoplayer` with the path to your local copy:
 
 ```gradle
-gradle.ext.exoplayerRoot = 'path/to/exoplayer'
 gradle.ext.exoplayerModulePrefix = 'exoplayer-'
-apply from: file("$gradle.ext.exoplayerRoot/core_settings.gradle")
+apply from: file("path/to/exoplayer/core_settings.gradle")
 ```
 
 You should now see the ExoPlayer modules appear as part of your project. You can

RELEASENOTES.md

@@ -17,6 +17,9 @@
     *   Fix `NullPointerException` being thrown from `CacheDataSource` when
         reading a fully cached resource with `DataSpec.position` equal to the
         resource length.
+    *   Fix a bug when [depending on ExoPlayer locally](README.md#locally) with
+        a relative path
+        ([#9403](https://github.com/google/ExoPlayer/issues/9403)).
 *   Extractors:
     *   Support TS packets without PTS flag
         ([#9294](https://github.com/google/ExoPlayer/issues/9294)).

core_settings.gradle

@@ -11,7 +11,7 @@
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-def rootDir = file(gradle.ext.exoplayerRoot)
+def rootDir = file(".")
 if (!gradle.ext.has('exoplayerSettingsDir')) {
     gradle.ext.exoplayerSettingsDir = rootDir.getCanonicalPath()
 }

settings.gradle

@@ -11,7 +11,6 @@
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-gradle.ext.exoplayerRoot = rootDir
 gradle.ext.exoplayerModulePrefix = ''
 
 def modulePrefix = ':'