fix(@angular/cli): propagate package manager errors when install fails - #34682

1. Defensive Programming: If e.stdout or e.stderr is undefined or null at runtime (e.g., in certain error scenarios or test environments), calling .trim() directly on them will throw a TypeError (e.g., Cannot read properties of undefined (reading 'trim')). This would crash the CLI and completely mask the original package manager error. Using optional chaining (?.) and nullish coalescing (??) prevents this secondary crash.

2. Preserving Non-PackageManagerError Context: If e is not an instance of PackageManagerError (e.g., a network failure, file system issue, or other unexpected error), the current implementation discards the original error message and throws a generic 'Unable to install packages' message. Appending the original error's message using assertIsError(e) ensures that valuable diagnostic context is not lost.

          } catch (e) {
            let message = 'Unable to install packages';
            if (e instanceof PackageManagerError) {
              const stdout = e.stdout?.trim() ?? '';
              const stderr = e.stderr?.trim() ?? '';
              message += `: ${colors.bold(e.message)}${
                stdout ? `\n\n${colors.bold('[STDOUT]')}: ${stdout}` : ''
              }${stderr ? `\n\n${colors.bold('[STDERR]')}: ${colors.red(stderr)}` : ''}`;
            } else {
              assertIsError(e);
              message += `: ${e.message}`;
            }

            throw new CommandError(message);
          }

Updated to always propagate errors and use assertIsError as suggested. @alan-agius4 can you confirm that assertIsError is appropriate? The assertion error would still surface an error, but would not include "Update to install packages". I assume the assertion error is unlikely to be triggered because the codebase probably consistently uses error objects rather than primitive types / non error objects.