chore: Refactor Gradle variables.

Author: DylanVann

android/build.gradle

@@ -14,18 +14,22 @@ def safeExtGet(prop, fallback) {
     rootProject.ext.has(prop) ? rootProject.ext.get(prop) : fallback
 }
 
-def _reactNativeVersion = safeExtGet("reactNative", "+")
+def _excludeAppGlideModule = safeExtGet("excludeAppGlideModule", false)
+def _buildToolsVersion = safeExtGet("buildToolsVersion", "28.0.3")
 def _compileSdkVersion = safeExtGet("compileSdkVersion", 28)
 def _glideVersion = safeExtGet("glideVersion", "4.9.0")
+def _minSdkVersion = safeExtGet("minSdkVersion", 16)
+def _reactNativeVersion = safeExtGet("reactNative", "+")
+def _targetSdkVersion = safeExtGet("targetSdkVersion", 28)
 
 android {
     compileSdkVersion _compileSdkVersion
-    buildToolsVersion safeExtGet("buildToolsVersion", "28.0.3")
+    buildToolsVersion _buildToolsVersion
 
     sourceSets {
         main {
             java {
-                if (safeExtGet("excludeAppGlideModule", false)) {
+                if (_excludeAppGlideModule) {
                     srcDir "src"
                     exclude "**/FastImageGlideModule.java"
                 }
@@ -34,8 +38,8 @@ android {
     }
 
     defaultConfig {
-        minSdkVersion safeExtGet("minSdkVersion", 16)
-        targetSdkVersion safeExtGet("targetSdkVersion", 28)
+        minSdkVersion _minSdkVersion
+        targetSdkVersion _targetSdkVersion
         versionCode 1
         versionName "1.0"
     }