android: add optional native host lifecycle hooks

tests/engine/android_host_extension_test.lua

@@ -0,0 +1,58 @@
+-- GameActivity exposes an optional Android host seam without requiring any
+-- host implementation (or its native libraries) in the stock build.
+-- Self-contained: luajit tests/engine/android_host_extension_test.lua
+local path = "mobile/android/love/src/main/java/org/love2d/android/GameActivity.java"
+local file = assert(io.open(path, "rb"))
+local source = file:read("*a")
+file:close()
+
+local function check(value, message)
+  if not value then error(message, 2) end
+end
+
+local function position(text)
+  local p = source:find(text, 1, true)
+  check(p, "missing: " .. text)
+  return p
+end
+
+check(source:find("protected String[] getHostLibraries()", 1, true),
+  "host libraries are an overridable protected extension")
+check(source:find("return new String[0];", 1, true),
+  "the vanilla host library list is empty")
+
+local cpp = position('libraries[0] = "c++_shared";')
+local mpg = position('libraries[1] = "mpg123";')
+local openal = position('libraries[2] = "openal";')
+local host = position("System.arraycopy(hostLibraries, 0, libraries, 3, hostLibraries.length);")
+local love = position('libraries[libraries.length - 1] = "love";')
+check(cpp < mpg and mpg < openal and openal < host and host < love,
+  "optional libraries load after dependencies while liblove remains last")
+
+for _, hook in ipairs({
+  "onHostCreateBeforeSDL", "onHostCreateAfterSDL", "onHostResume",
+  "onHostPause", "onHostDestroy",
+}) do
+  check(source:find("protected void " .. hook, 1, true),
+    hook .. " is a protected extension hook")
+end
+
+check(position("onHostCreateBeforeSDL(savedInstanceState);") <
+      position("super.onCreate(savedInstanceState);") and
+      position("super.onCreate(savedInstanceState);") <
+      position("onHostCreateAfterSDL(savedInstanceState);"),
+  "create hooks bracket SDL creation")
+check(position("super.onResume();") < position("onHostResume();"),
+  "resume hook runs after SDL resumes")
+check(position("onHostPause();") < position("super.onPause();"),
+  "pause hook runs before SDL pauses")
+check(position("onHostDestroy();") < position("super.onDestroy();"),
+  "destroy hook runs before SDL destruction")
+
+check(not source:lower():find("openxr", 1, true),
+  "generic Android activity must not require OpenXR")
+check(not source:find("QuestActivity", 1, true) and
+      not source:find("QuestBridge", 1, true),
+  "generic Android activity must not require Quest classes")
+
+print("android_host_extension_test: ok")