android: use the native system keyboard for menu text entry

[LibretroAdmin]

This replaces #19126

my bad @Keropon , this was the only way I saw to still salvage the PR

Guidelines

• Rebase before opening a pull request
• If you are sending several unrelated fixes or features, use a branch and a separate pull request for each
• If possible try squashing everything in a single commit. This is particularly beneficial in the case of feature merges since it allows easy bisecting when a problem arises
• RetroArch codebase follows C89 coding rules for portability across many old platforms check using C89_BUILD=1

Description

Adds an option to use the native Android system keyboard (IME) for menu text entry instead of RetroArch's built-in on-screen keyboard, bringing Android to parity with iOS (which already swaps in the native keyboard via ios_keyboard_start()).

Why

The built-in OSK only ever receives hardware key events. On Android's NativeActivity there is no text field, so IME-committed text like clipboard paste, password-manager autofill, autocomplete, swipe, will never reach it. Pasting is therefore impossible in fields like the RetroAchievements login, menu Search, and cheat-code entry.

How it works (mirrors the existing iOS path):

• New setting Settings → Input → "Use System Keyboard" gates the feature. Defaults OFF, so gamepad-only / no-touch devices (e.g. Android TV) keep the gamepad-navigable on-screen keyboard unless they opt in.
• When enabled, menu_input_dialog_start() / menu_input_dialog_start_search() call a new android_keyboard_start(), placed alongside the existing #ifdef HAVE_COCOATOUCH iOS hooks.
• RetroActivityCommon raises the soft keyboard through a hidden, focusable EditText overlay and forwards committed/pasted text back via a new onSystemKeyboardInput() JNI callback.
• The IME runs on the Android UI thread, so text is staged under a lock and applied on the RetroArch input thread in android_keyboard_poll() (drained from android_input_poll()), then fed into the existing input_keyboard_line; The rest of the menu code is unchanged.

Scope / notes:

• Menu OSK text entry only; in-game (core) keyboard input is untouched; Same scope as the iOS implementation.
• Verified C89-clean on the Android NDK build (-std=gnu89 -Wdeclaration-after-statement); no new warnings introduced by the added code.

Related Issues

• Addresses (Menu) Add Copy/Paste Support to On-Screen Keyboard #10244 on Android
• Addresses Cannot paste into RetroAchievements login password entry field. #15824 on Android

Related Pull Requests

None.

Reviewers

[Will update later]

Video Example

Tested on a Retroid Pocket Classic (Android 14)

screen-20260619-005333.mp4