Fixes #9001.

Summary

When io.ConfigInputTextEnterKeepActive is enabled, pressing Enter on a single-line InputText keeps the widget active and selects the contents.
However, in this mode the item is never considered "deactivated", so IsItemDeactivatedAfterEdit() never fires and existing undo/finalization logic breaks.

Issue

• Without ConfigInputTextEnterKeepActive:
  • Pressing Enter deactivates the item, and IsItemDeactivatedAfterEdit() becomes true for one frame.
• With ConfigInputTextEnterKeepActive:
  • Pressing Enter keeps the item active, and IsItemDeactivatedAfterEdit() is never triggered.
• This is the situation described in IsItemDeactivatedAfterEdit doesn't play nicely with ConfigInputTextEnterKeepActive #9001, where code that relies on IsItemDeactivatedAfterEdit() to finalize edits stops working.

Fix

• On Enter, when ConfigInputTextEnterKeepActive is set, I:
  • Let the widget go through the normal "deactivated after edit" path so that IsItemDeactivatedAfterEdit() is signaled as usual.
  • Immediately reactivate the same InputText for the next frame and select its contents.
• This preserves the existing idiomatic use of IsItemDeactivatedAfterEdit() while keeping the behavior promised by ConfigInputTextEnterKeepActive.

Testing

• Reproduced the behavior described in IsItemDeactivatedAfterEdit doesn't play nicely with ConfigInputTextEnterKeepActive #9001:
  • IsItemDeactivatedAfterEdit() never triggered with ConfigInputTextEnterKeepActive enabled.
• Verified after the patch:
  • IsItemDeactivatedAfterEdit() is true for one frame when pressing Enter, even with the config flag set.
  • Focus remains on the input and text is selected as before.
• Also checked:
  • Pressing Enter without ConfigInputTextEnterKeepActive (unchanged behavior).
  • Clicking outside the widget to deactivate.
  • No regressions observed in basic InputText examples.