cmake: Capture more complete configure/generate steps in printed durations

Extend the start/end times from commit 5f0c5ec49b (cmake: Print
configure/generate time, 2023-01-17, v3.26.0-rc1~67^2) to capture
generator-specific Configure/Generate actions, and the time spent
in the internal "Compute" step at the start of generation.

Fixes: #25482