android: Avoid icon name clash with material library

Rename the file for the keyboard icon from
`ic_keyboard_black_24dp.png` to
`ic_keyboard_black__24dp.png` (note the extra underscore)
to avoid a name clash with an icon of the same name
in the Material components: [1]

Keeping the same name would result in this lint error when
upgrading to material 1.11.0 (which an upcoming commit will
do):

    > Task :lintStrippedUIEditingDebug FAILED
    /home/michi/development/git/libreoffice-WORKTREE-android/android/source/lint-baseline.xml: Information: 213 errors and 1 warning were filtered out because they are listed in the baseline file, lint-baseline.xml
     [LintBaseline]
    /home/michi/development/git/libreoffice-WORKTREE-android/android/source/lint-baseline.xml: Information: 6 errors/warnings were listed in the baseline file (lint-baseline.xml) but not found in the project; perhaps they have been fixed? Another possible explanation is that lint recently stopped analyzing (and including results from) dependent projects by default. You can turn this back on with android.lintOptions.checkDependencies=true. Unmatched issue types: PrivateResource, RedundantNamespace, TypographyEllipsis (3), UnusedNamespace [LintBaseline]
    /home/michi/development/git/libreoffice-WORKTREE-android/android/source/res/drawable-hdpi/ic_keyboard.xml:4: Error: The resource @drawable/ic_keyboard_black_24dp is marked as private in com.google.android.material:material:1.11.0 [PrivateResource]
        android:src="@drawable/ic_keyboard_black_24dp"
                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

       Explanation for issues of type "PrivateResource":
       Private resources should not be referenced; the may not be present
       everywhere, and even where they are they may disappear without notice.

       To fix this, copy the resource into your own project instead.

    1 errors, 0 warnings (213 errors, 1 warning filtered by baseline lint-baseline.xml)

(For the currently-used material 1.10.0, this warning was previously
ignored since it's already listed in the lint-baseline.xml file, but that doesn't
apply any more after an update.)

[1] https://github.com/material-components/material-components-android/blob/bb351291a360319df31d5cee27e091c3e64f65a4/lib/java/com/google/android/material/timepicker/res/drawable/ic_keyboard_black_24dp.xml

Change-Id: I2babc445c69f1043967118be81905c334a0285d2
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/161889
Tested-by: Jenkins
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>

android/source/res/drawable-hdpi/ic_keyboard.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 
 <bitmap xmlns:android="http://schemas.android.com/apk/res/android"
-    android:src="@drawable/ic_keyboard_black_24dp"
-    android:tint="@color/toolbar_foreground"/>
+    android:src="@drawable/ic_keyboard_black__24dp"
+    android:tint="@color/toolbar_foreground"/>