Python API for Render Time

Every image rendered in Blender has associated data for how long that frame took to render: it's shown in the render window, it can be printed to the terminal, and it's saved in the metadata of the file itself.

However, this doesn't seem to be accessible from the Python API in any way. Would be super helpful for plugins like those that auto save rendered images (they could include render time in the file name) and title render time estimates (more easily accessing render times without having to run timers constantly).

Proposal: add completed render time access to the Python API. Even better, add all image metadata for additional use cases.