fix(cli/fmt_errors): don't panic on source line formatting errors (#12449)

Returns empty values in case of errors, source lines are non-essential anyway. These errors can happen e.g. when source files change at runtime. A warning is also printed to help us track when it happens in unexpected cases besides this.

cli/tests/testdata/eval_context_throw_with_conflicting_source.ts

@@ -0,0 +1,6 @@
+// deno-lint-ignore no-explicit-any
+const [, errorInfo] = (Deno as any).core.evalContext(
+  '/* aaaaaaaaaaaaaaaaa */ throw new Error("foo")',
+  new URL("eval_context_conflicting_source.ts", import.meta.url).href,
+);
+throw errorInfo.thrown;