fix(android): the window shrinks for the keyboard, so forms can scroll

Measured, after two fixes placed by reasoning changed nothing:

  focus: inner 719 visual 719 | box client 659 scroll 659 | body=on-detail

Keyboard up, and both heights unchanged: the page has no way to learn the
keyboard exists - visualViewport reports nothing here either. And the box
shows 659 for 659 of content, so there is no overflow and nothing can
scroll. The keyboard simply covers the bottom of a page that believes it
still has the whole screen.

So the remedy was never in the page. windowSoftInputMode="adjustResize"
makes the window itself shrink; the scroll box then gets real overflow and
the engine can bring the focused field into view on its own.

The reserve added below the scroll area stays: it costs nothing when the
window does resize (the measure is then zero), and it is the honest place
for the value should a device ever report it.

AndroidManifest.template.xml

@@ -63,11 +63,21 @@
 <%services%>
         <!-- Our activity is a subclass of the built-in NativeActivity framework class.
              This will take care of integrating with our NDK code. -->
+        <!-- windowSoftInputMode : LA FENETRE SE RETRECIT QUAND LE CLAVIER MONTE.
+             Sans cela il RECOUVRE la page - le cadre garde sa hauteur, le
+             contenu ne deborde de rien, et le bas du formulaire devient
+             inatteignable : le champ mot de passe ne se voyait qu'en repliant
+             le clavier. Mesure a l'appui, clavier leve : innerHeight et
+             visualViewport.height restaient tous deux a 719, et la boite
+             defilante montrait 659 pour 659 de contenu. La page n'avait aucun
+             moyen d'apprendre que le clavier existait ; c'est la fenetre qui
+             devait le dire. -->
         <activity
             android:name="com.embarcadero.firemonkey.FMXNativeActivity"
             android:exported="true"
             android:label="%activityLabel%"
             android:configChanges="orientation|keyboard|keyboardHidden|screenSize|screenLayout|uiMode"
+            android:windowSoftInputMode="adjustResize"
             android:launchMode="singleTask">
             <!-- Tell NativeActivity the name of our .so -->
             <meta-data android:name="android.app.lib_name" android:value="%libNameValue%" />