Blender Git Loki

Fix T82002: ENTER does nothing when mouse cursor is over save dialog text field

The `file.execute` operator would early-exit because the mouse wasn't hovering
the file list. Caused by 4ba9d7d71e8f.

Although simpler solutions would have been possible, I decided it's better to
split add a new operator for executing based on the mouse (for double-clicking
files), to separate that from the window level execute operator
(`file.execute`). This allows more control and we can get rid of the implicit
assumption that the keymap would call `file.select` on mouse-press, and
`file.execute` on double-click, for the double-click behavior to work. The cost
is that we execute the file selection & activation logic twice on the
double-click, but that shouldn't be an issue at all.
Also removes the `need_active` property from the `file.execute` operator.
That's ancient and wasn't implemented well anyway.

To be clear, reason this fixes the bug is that `file.execute` works entirely
with the `execute()` callback now and doesn't early-exit based on the mouse
position anymore.

Might trigger warnings about the `need_active` property not being found for
custom keymaps. These can be ignored and the property can safely be removed
from the keymap. I don't expect other keymap breakages.