Add logic to publish the Godot OpenXR Android library to MavenCentral

[m4gr3d]

This PR follows the instructions from https://getstream.io/blog/publishing-libraries-to-mavencentral-2021/ to setup the logic to publish the Godot OpenXR Android Library to MavenCentral.

MavenCentral is a repository provided by the Maven community which contains a large number of commonly used libraries.
It's an important tool for java and Android developers as it simplifies the resolution and fetching process for a project's dependencies by build tools like Gradle.

The updated logic will enable to push (automatically) the generated Godot OpenXR Android library to MavenCentral so that users can access it by adding a single line to their gradle build file:

dependencies {
    ...
    implementation 'io.github.m4gr3d:godot-openxr:<versions>'
    ...
}

Publishing To MavenCentral

• This requires a sonatype account and a GPG key to sign the generated library.
• Provide values for the variables defined in publish-root.gradle. This can either be done via environment variables, or through the local.properties file (that file is not and should not be added to git).
• Generate the Godot OpenXR Android library via the usual build process.
• Run the following commands to push the generated library to MavenCentral:
  • ./gradlew publishFullReleasePublicationToSonatypeRepository
• Follow these steps to review the uploaded binary and release it publicly on MavenCentral.

Notes & TODOs

• I'm using my own sonatype credentials at the moment to publish the library. Eventually, we would want to switch to GodotVR's own set of credentials.
• Automatic publishing is blocked by above todo. Once we have a set of credentials for GodotVR, we can automate the publishing of the Godot Android Library by leveraging github workflows as described here.
• Update OpenXR Android related documentation accordingly.

Part of #191

[BastiaanOlij]

Should this be m4gr3d? not GodotVR once merged?

[m4gr3d]

This is the dependency for the Godot Android library. For now until godotengine/godot-proposals#4230 is completed, I'm using my own sonatype account hence why it's io.github.m4gr3d.

Once godotengine/godot-proposals#4230 is complete, it will be switched to something like org.godotengine:godot:<version>.

[m4gr3d]

fyi, I've added #191 to track the remaining steps.

[BastiaanOlij]

Cool!