Screenshot fails with long view / Screenshot functionality missing

### Description
When using the `Screenshot.capture(view)` method on a long constraint layout (I had a need to capture the full content of a long scroll view), an exception is thrown due to `View.getDrawingCache()` returning `null`. As far as I can tell from research this can occur in views that result in a large bitmap, the `getDrawingCache()` method just gives up.

I tried a number of workarounds but the only effective one has been to draw the view to bitmap by doing a measure, layout, `draw(canvas)` approach. Unfortunately there is no mechanism in `Screenshot` to do things this way, `ScreenCapture` also has a package-private constructor, and the set of processors in `Screenshot` are private, making it difficult to extend the behaviour to accommodate different capture methods. In the end I resorted to defining a hacky extension in the `androidx.test.runner.screenshot` package in my project.

This exposes a functionality gap in the Screenshot class and I'd suggest (and am happy to work on) a variant of of `Screenshot.capture` that either captures the bitmap using the `View.draw` method or takes a function allowing the API user to specify their own bitmap creation allowing easier reuse of the rest of the Screenshot functionality (processing and writing to file).

### AndroidX Test and Android OS Versions
runner 1.3.0

Start with Screenshot.capture(view), then inspect ScreenCapture and the private processors described in the issue to understand the existing capture, processing, and file-writing flow. Done means exposing a supported capture variant that handles long views without getDrawingCache() returning null while preserving the existing processing and file output behavior.

Written by the indexing model from the issue text.