Issue Description:

This implementation of conversion from String to Data is in some cases 900x faster by taking advantage of fast paths. Ideally we should not drop performance like this on the floor and offer fast access to the appropriate backing storage. (note this is just a draft/toy version of what it should be but the concept should be implemented as API or SPI).

See the example at: https://gist.github.com/phausler/c6178bc9b0764f51d3ac182a293cede5