[Eva] api: Add Analysis.{compute,is_computed}

Makefile

src/plugins/value/Eva.mli

src/plugins/value/api/general_requests.ml

src/plugins/value/engine/analysis.ml

src/plugins/value/engine/analysis.mli

src/plugins/value/gui_files/gui_callstacks_manager.ml

src/plugins/value/gui_files/gui_eval.ml

src/plugins/value/gui_files/register_gui.ml

src/plugins/value/register.ml

src/plugins/value/utils/value_results.mli