Migrate constructors to builder lambdas for future-proof configuration

[russhwolf]

This feels unnecessary for implementations that just take a single delegate argument in the constructor, but as more config options become available (eg threading options in AppleSettings, commit vs apply flag in AndroidSettings), I'd like to consider it more deeply to avoid backward-compatibility issues.

kotlinx.serialization did this in preparation for 1.0: https://youtu.be/Azi57n59ICM?t=555
See also https://jakewharton.com/public-api-challenges-in-kotlin/