Base+Utilities: Add run-tests program to run system tests with LibTest

This test program heavily pulls from the JavaScriptTestRunner/test-js,
but with a twist. Instead of loading JavaScript files into the current
process, constructing a JS environment for them, and executing test
suites/tests directly, run-tests posix_spawns each test file.

Test file stdout is written to a temp file, and only dumped to console
if the test fails or the verbose option is passed to the program. Unlike
test-js, times are always printed for every test executed for better
visibility in CI.

Userland/Libraries/LibTest/Results.h

@@ -17,6 +17,7 @@ enum class Result {
     Pass,
     Fail,
     Skip,
+    Crashed,
 };
 
 struct Case {