Move prebuilt-deps/ to app/

The prebuilt dependencies are specific to the client app (not the
server).

This also avoids to reference the parent directory (../) from
app/meson.build.

app/prebuilt-deps/prepare-adb.sh

@@ -0,0 +1,32 @@
+#!/usr/bin/env bash
+set -e
+DIR=$(dirname ${BASH_SOURCE[0]})
+cd "$DIR"
+. common
+mkdir -p "$PREBUILT_DATA_DIR"
+cd "$PREBUILT_DATA_DIR"
+
+DEP_DIR=platform-tools-31.0.3
+
+FILENAME=platform-tools_r31.0.3-windows.zip
+SHA256SUM=0f4b8fdd26af2c3733539d6eebb3c2ed499ea1d4bb1f4e0ecc2d6016961a6e24
+
+if [[ -d "$DEP_DIR" ]]
+then
+    echo "$DEP_DIR" found
+    exit 0
+fi
+
+get_file "https://dl.google.com/android/repository/$FILENAME" \
+    "$FILENAME" "$SHA256SUM"
+
+mkdir "$DEP_DIR"
+cd "$DEP_DIR"
+
+ZIP_PREFIX=platform-tools
+unzip "../$FILENAME" \
+    "$ZIP_PREFIX"/AdbWinApi.dll \
+    "$ZIP_PREFIX"/AdbWinUsbApi.dll \
+    "$ZIP_PREFIX"/adb.exe
+mv "$ZIP_PREFIX"/* .
+rmdir "$ZIP_PREFIX"