android: integrate gradle task to build loleaflet

Change-Id: I6f2d39d7986d3f9e477bad225e554c3bdb71d125
Reviewed-on: https://gerrit.libreoffice.org/c/online/+/92598
Tested-by: Jenkins CollaboraOffice <jenkinscollaboraoffice@gmail.com>
Reviewed-by: Henry Castro <hcastro@collabora.com>

android/app/build.gradle

@@ -72,3 +72,11 @@ dependencies {
     implementation 'androidx.preference:preference:1.1.0-alpha01'
     implementation project(path: ':lib')
 }
+
+task build_loleaflet(type: Exec) {
+	commandLine 'make', '-C', '../../'
+}
+
+afterEvaluate {
+	preBuild.dependsOn build_loleaflet
+}