Android: add RetroAchievements host override receiver

[misantronic]

RAOfflineProxy is an Android app that proxies RetroAchievements traffic through 127.0.0.1, enabling offline softcore achievement play through local caching and later sync.

On Android, controlling the RetroAchievements host override through a broadcast receiver is a cleaner integration point than relying on external tools to patch retroarch.cfg directly.

This makes the host override controllable by another Android app at runtime instead of requiring external file edits, which is more brittle and harder to integrate cleanly.

Summary

• Add an Android broadcast receiver for setting and clearing the RetroAchievements host override
• Persist the override across app restarts
• Apply host and hardcore changes live while RetroArch is already running
• Disable hardcore while the override is active and restore the prior hardcore preference when clearing the override
• Refresh the Achievements menu after live changes so the updated settings are reflected immediately

Testing

• Built and installed the Android aarch64 debug build on device
• Verified SET_RETROACHIEVEMENTS_HOST_OVERRIDE persists cheevos_custom_host and applies the override live while RetroArch is open
• Verified the live apply path disables hardcore while the override is active
• Verified CLEAR_RETROACHIEVEMENTS_HOST_OVERRIDE removes the stored override, reapplies the default host live, and restores the prior hardcore preference
• Verified the host-override broadcasts do not restart the RetroArch process

Related

• Same Android host-override integration already merged for ARMSX2 and released in a nightly build
• Same Android host-override integration already merged for PPSSPP and planned for the next release
• Same Android host-override integratin already merged for flycast and currently in the development build
• Same integration proposed for Dolphin
• Same integration proposed for melonDS
• Same integration planned for melonDualDS

[misantronic]

The msys2-build-test (MINGW64) job failed after 28 seconds while downloading MSYS2, before any compilation started. It's unrelated to the changes in this PR. Could a maintainer re-run that job?

[misantronic]

To provide a bit more context and an update on this topic: Recently, SapphireRhodonite, the developer of melonDualDS, contacted me, and they plan to include it in their next version of melonDualDS as well.
Also, the author of flycast merged my pull request, and it's already in their development build.

RetroArch is the biggest system in the business, and support for host override receiver would be fantastic!

[hizzlekizzle]

@LibretroAdmin I spoke with Jamiras about this to make sure the RetroAchievements folks are okay with it, and he said they were, so we don't need to worry about this stepping on anyone's toes in that respect.