Fix review feedback: use exec, WSLC_TEST_METHOD, and full path in test

Address review feedback:
- Use 'exec' to replace the shell process instead of spawning a child
  process (OneBlue, Copilot)
- Use WSLC_TEST_METHOD macro so the test only runs in the WSLC test
  suite, not WSL1/WSL2 suites where wslc.exe is unavailable
- Use GetMsiPackagePath() + wslpath to resolve the full path to
  wslc.exe and wslc script, since the install directory may not be
  on PATH in CI

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Ben Hillis

src/windows/wslc/wslc

@@ -8,5 +8,4 @@
 WSL_PATH="$(dirname "$(realpath "$0")")"
 WSLC_EXE="$WSL_PATH/wslc.exe"
 
-"$WSLC_EXE" "$@"
-exit $?
+exec "$WSLC_EXE" "$@"

test/windows/SimpleTests.cpp

@@ -295,12 +295,16 @@ class SimpleTests
         VERIFY_IS_TRUE(output.find(L"/mnt/c/Users/Test User/AppData/Local/Programs/Microsoft VS Code/bin") != std::wstring::npos);
     }
 
-    TEST_METHOD(WslcShellScript)
+    WSLC_TEST_METHOD(WslcShellScript)
     {
         // Verify that the 'wslc' shell script (no .exe extension) invokes wslc.exe
         // and produces the same output as calling wslc.exe directly.
-        auto [exeOutput, exeErr] = LxsstuLaunchWslAndCaptureOutput(L"wslc.exe version");
-        auto [scriptOutput, scriptErr] = LxsstuLaunchWslAndCaptureOutput(L"wslc version");
+        // Use the full install path since the MSI directory may not be on %PATH% in CI.
+        auto installPath = wsl::windows::common::wslutil::GetMsiPackagePath().value();
+        auto exeCmd = std::format(L"$(wslpath '{}wslc.exe') version", installPath);
+        auto scriptCmd = std::format(L"$(wslpath '{}wslc') version", installPath);
+        auto [exeOutput, exeErr] = LxsstuLaunchWslAndCaptureOutput(exeCmd);
+        auto [scriptOutput, scriptErr] = LxsstuLaunchWslAndCaptureOutput(scriptCmd);
         VERIFY_ARE_EQUAL(exeOutput, scriptOutput);
         VERIFY_ARE_EQUAL(exeErr, scriptErr);
     }