Include Android app name in handshake metadata

[samsamtrum]

Summary

Adds the Android app label to the handshake payload so wallets can display a recognizable dapp name instead of relying only on the package id.

Problem

RequestContent.Handshake already supports optional appName, but the Android native SDK never populated it. As a result, wallet confirmation/connection surfaces can receive only the package identifier (appId), which is less readable for end users and can be inconsistent with the iOS/JS-facing expectation that apps may provide display metadata.

Changes

• Resolve the host app label from Context.applicationInfo / PackageManager.
• Pass that label as appName when building the Android handshake message.
• Keep backward compatibility by exposing appName as an optional parameter with the app label as the default, so callers can still override or omit it.

Verification

• git diff --check passes.
• Attempted Android compile/test with:
  • JAVA_HOME=/usr/lib/jvm/java-17-openjdk-amd64 ./gradlew :walletsdk:compileDebugKotlin :walletsdk:testDebugUnitTest --stacktrace
• The local environment is missing Android SDK / ANDROID_HOME, so Gradle cannot resolve the Android SDK location before compiling. No project test failures were reached.