upstream PR to have tab view in memory

[matu3ba]

Alternatives to consider:

• 1. A very annoying workaround is to use mksession and parse the output file.
• 2. Upstream patch to print into register or buffer with lua function
• 3. the no upper time backtracking algorithm to reconstruct how windows were split

Use a simpler approach (only 1 split supported) and fix, when more users.