Allowed passing customized icon for completed steps in `Stepper` #14280

All 1 187 tests pass in 3m 41s

1 files ±0 133 suites ±0 3m 41s ⏱️ +2s
1 187 tests ±0 1 187 ✅ ±0 0 💤 ±0 0 ❌ ±0
1 209 runs ±0 1 209 ✅ ±0 0 💤 ±0 0 ❌ ±0

Results for commit eadac89. ± Comparison against earlier commit 567e6ab.