core: Handle ProxySelector IllegalArgumentException

[kkmurthyt21]

Fixes #13052.

Android’s DefaultProxySelector.select() may throw IllegalArgumentException when the system proxy configuration contains an invalid port. This unchecked exception currently escapes the DNS resolver task and can terminate the process.

This change catches the exception at the ProxySelector.select() call and wraps it in an IOException. The original cause is preserved, and the exception message identifies the ProxySelector implementation.

DnsNameResolver already handles an IOException from proxy detection as an UNAVAILABLE name-resolution result. This allows the resolver to fail cleanly instead of letting the unchecked exception escape.

This intentionally avoids silently falling back to a direct connection. It follows the fail-cleanly approach used for invalid ProxySelector results in #12793 and avoids bypassing a configured proxy.

Testing

1. Added a regression test verifying that the exception is wrapped, the original cause is preserved, and the ProxySelector implementation is identified.
2. Ran .\gradlew.bat :grpc-core:test --tests "io.grpc.internal.ProxyDetectorImplTest"
3. All 11 tests passed on Windows with Temurin JDK 17.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: kkmurthyt21 / name: Krishna Kandi (bc01614)