cppwinrt should consistently panic on failure

[kennykerr]

This brings the cppwinrt crate in line with the windows-bindgen crate that consistently panics on failure. As a build tool, this is simpler to consume and provides more reliable build failure information.

Copilot reviewed 5 out of 7 changed files in this pull request and generated no comments.

Files not reviewed (2)

• crates/tests/winrt/noexcept/build.rs: Evaluated as low risk
• crates/tests/winrt/ref_params/build.rs: Evaluated as low risk

Comments suppressed due to low confidence (2)

crates/libs/cppwinrt/src/lib.rs:32

• The panic message should provide more context. Consider changing it to panic!("cppwinrt failed: {}", String::from_utf8_lossy(&output.stderr)).

panic!("{}", String::from_utf8_lossy(&output.stderr))

crates/libs/cppwinrt/src/lib.rs:42

• Ensure that the new behavior of panicking on failure is adequately covered by tests. The invalid_arg test should cover this scenario.

fn invalid_arg() {