gradle: Factor out the dependency versions to a build-wide variable

build.gradle

@@ -2,8 +2,19 @@
 // SPDX-License-Identifier: BSL-1.0
 
 buildscript {
-    ext.kotlin_version = '1.4.10'
-    ext.latestAboutLibsRelease = "8.5.0"
+    ext {
+        kotlinVersion = '1.4.10'
+        latestAboutLibsRelease = "8.5.0"
+
+        androidxCoreVersion = "1.3.2"
+        androidxAnnotationVersion = "1.1.0"
+        androidxAppCompatVersion = "1.2.0"
+        androidxLifecycleVersion = "2.2.0"
+        androidxConstraintLayoutVersion = '2.0.4'
+
+        // Saw some breakage when updating to 1.2?
+        materialVersion = "1.1.0"
+    }
     repositories {
         google()
         jcenter()
@@ -11,7 +22,7 @@ buildscript {
     }
     dependencies {
         classpath 'com.android.tools.build:gradle:4.1.0'
-        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlinVersion"
         classpath "com.mikepenz.aboutlibraries.plugin:aboutlibraries-plugin:${latestAboutLibsRelease}"
     }
 }

src/xrt/auxiliary/android/build.gradle

@@ -26,5 +26,5 @@ android {
 }
 
 dependencies {
-    implementation 'androidx.annotation:annotation:1.1.0'
+    implementation "androidx.annotation:annotation:$androidxAnnotationVersion"
 }

src/xrt/ipc/android/build.gradle

@@ -28,5 +28,5 @@ android {
 
 dependencies {
     implementation project(':src:xrt:auxiliary:android')
-    implementation 'androidx.annotation:annotation:1.1.0'
+    implementation "androidx.annotation:annotation:$androidxAnnotationVersion"
 }

src/xrt/targets/openxr_android/build.gradle

@@ -132,13 +132,15 @@ aboutLibraries {
 dependencies {
     outOfProcessImplementation project(':src:xrt:ipc:android')
     implementation project(':src:xrt:auxiliary:android')
-    implementation 'androidx.appcompat:appcompat:1.2.0'
-    implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
-    implementation 'androidx.constraintlayout:constraintlayout:2.0.3'
+    implementation "androidx.appcompat:appcompat:$androidxAppCompatVersion"
+    implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlinVersion"
+    implementation "androidx.constraintlayout:constraintlayout:$androidxConstraintLayoutVersion"
+    implementation "com.google.android.material:material:$materialVersion"
+
+    // Dependencies related only to AboutLibraries
     implementation "com.mikepenz:aboutlibraries-core:${latestAboutLibsRelease}"
     implementation "com.mikepenz:aboutlibraries:${latestAboutLibsRelease}"
     implementation "androidx.cardview:cardview:1.*.*"
     implementation "androidx.recyclerview:recyclerview:1.1.*"
-    implementation "com.google.android.material:material:1.1.*"
 
 }