perf: avoiding use of Object.defineProperty in Chunk constructor

[rsystancia]

As described here https://humanwhocodes.com/blog/2015/11/performance-implication-object-defineproperty/
Object.defineProperty does add some overhead.

This can become significant when a lot of splitting is involved.

This PR restrict the usage of Object.defineProperty in DEBUG only.

A benchmark using overwrite has been added, an show significant improvement.
other benchmarks have been improved too.

before

construct x 78,561 ops/sec ±0.50% (93 runs sampled)
append x 5,732,848 ops/sec ±5.76% (44 runs sampled)
indent x 2,386 ops/sec ±1.50% (89 runs sampled)
generateMap (no edit) x 1,283 ops/sec ±1.86% (89 runs sampled)
generateMap (edit) x 1,346 ops/sec ±0.76% (93 runs sampled)
generateDecodedMap (no edit) x 1,604 ops/sec ±1.07% (92 runs sampled)
generateDecodedMap (edit) x 1,574 ops/sec ±1.12% (90 runs sampled)
overwrite x 0.67 ops/sec ±2.38% (6 runs sampled)

after

construct x 95,813 ops/sec ±0.51% (95 runs sampled)
append x 5,992,517 ops/sec ±5.10% (62 runs sampled)
indent x 2,624 ops/sec ±1.64% (89 runs sampled)
generateMap (no edit) x 1,331 ops/sec ±1.40% (91 runs sampled)
generateMap (edit) x 1,355 ops/sec ±0.62% (94 runs sampled)
generateDecodedMap (no edit) x 1,664 ops/sec ±0.40% (95 runs sampled)
generateDecodedMap (edit) x 1,650 ops/sec ±0.83% (96 runs sampled)
overwrite x 2.31 ops/sec ±3.67% (10 runs sampled)