(draft PR because this is currently sitting atop an early version of #13741 that is necessary to get some of the results; please ignore those commits, they will be rebased away once that PR is merged)

Model withUnsafeBytes and some similar closure methods.

Limitations:

• I've used .ArrayContent to access content when we know the Collection is an Array. I've used two models - one with .ArrayContent and one with no content specifier - when the object could be an Array or another type of Collection. I've used no content specifier for pointers (UnsafePointer etc) since we don't have content for any of those (yet). Thus, some level of conflation (e.g. between ptr and ptr[0]) is inevitable at this stage. We should be able to improve accuracy as we implement further types of content flow.
• another limitation is that certain methods and fields used in some of the tests (e.g. .baseAddress) are not yet modelled. There is an in-progress issue for these.
• I'm not sure why taint from array elements isn't always flowing into closures, e.g. in int.swift line 19. It works if the qualifier is a tainted array, but not if it's an array with tainted content as in the test (despite there being models for both cases).
  • update: there's a fix in another PR that very likely addresses this.

TODO:

• rebase atop final Swift: add DataFlow::Content for arrays #13741
• add change note
• may will also benefit from 098db58 (for missing test results such as int.swift line 19)