Refactor build system

The client was built with Meson, the server with Gradle, and were run by
a Makefile.

Add a Meson script for the server (which delegates to Gradle), and a
parent script to build and install both the client and the server to the
system, typically with:

    meson --buildtype release build
    cd build
    ninja
    sudo ninja install

In addition, use a separate Makefile to build a "portable" version of
the application (where the client expects the server to be in the
current directory). Typically:

    make release-portable
    cd dist/scrcpy
    ./scrcpy

This is especially useful for Windows builds, which are not "installed".

server/meson.build

@@ -0,0 +1,11 @@
+project('scrcpy-server', 'c')  # not really c, but meson expects something
+
+# does not track dependencies, so meson does not guarantees that server is up to date
+# call "touch server" or "ninja -t clean server/scrcpy-server.jar" before to rebuild
+custom_target('scrcpy-server',
+              build_always: false, # do not enable, otherwise "sudo ninja install" will execute gradle!
+              input: '.',
+              output: 'scrcpy-server.jar',
+              command: [find_program('./scripts/build-wrapper.sh'), '@INPUT@', '@OUTPUT@', get_option('buildtype')],
+              install: true,
+              install_dir: 'share/scrcpy')

server/scripts/build-wrapper.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+# Wrapper script to invoke gradle from meson
+set -e
+
+PROJECT_ROOT="$1"
+OUTPUT="$2"
+BUILDTYPE="$3"
+
+# gradlew is in the parent of the server directory
+GRADLE=${GRADLE:-$PROJECT_ROOT/../gradlew}
+
+if [[ "$BUILDTYPE" == debug ]]
+then
+    "$GRADLE" -p "$PROJECT_ROOT" assembleDebug
+    cp "$PROJECT_ROOT/build/outputs/apk/debug/server-debug.apk" "$OUTPUT"
+else
+    "$GRADLE" -p "$PROJECT_ROOT" assembleRelease
+    cp "$PROJECT_ROOT/build/outputs/apk/release/server-release-unsigned.apk" "$OUTPUT"
+fi