Skip file writes if files don’t change (and --serve client reloads too)

zachleat

If a file’s output hasn’t changed, don’t write it in the output folder (during `--watch` and `--serve` mode only). If a file’s output hasn’t changed, don’t reload client browsers when using the dev server either.

zachleat

Required downstream changes in dev server dependency: https://github.com/11ty/dev-server/releases/tag/v3.0.0-alpha.12

zachleat

Shipping with v4.0.0-alpha.11