Link libinput statically for inputflinger_tests

Linking statically makes it easier to debug tests by letting developer
add logs to libinput and have that reflected in the 'atest' runs for
inputflinger_tests without having to resync.

Also in this CL, enable C++20 for libinput, which would allow us to do
things like specify the default comparison operator.

Bug: 167946763
Test: cd services/inputflinger && atest
Change-Id: Iaa3f2e34d79fa000ef42b74237efae6233b44674
diff --git a/libs/input/Android.bp b/libs/input/Android.bp
index e73c3b8..930d819 100644
--- a/libs/input/Android.bp
+++ b/libs/input/Android.bp
@@ -35,6 +35,7 @@
 
 cc_library {
     name: "libinput",
+    cpp_std: "c++20",
     host_supported: true,
     cflags: [
         "-Wall",