need PRE_STEP_TCL variables to be implemented

[Cronus-38]

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Description

Currently there are a number of POST_STEP_TCL variables available in ORFS, including POST_FLOORPLAN_TCL and POST_CTS_TCL. These variables enable the user to source custom scripts at various points in the flow. It would be very helpful to have similar "PRE_" variables available throughout the flow.

Suggested Solution

As an example, currently in order to redefine a procedure that is called during execution of the cts.tcl script I need to either hack the cts.tcl script itself or hack the load.tcl script (which contains the pre-defined procedure I'm trying to redefine). It would be a much more elegant solution to have a PRE_CTS_TCL variable which points to a script that gets sourced after the load.tcl file is sourced at the beginning of the cts.tcl script. This would avoid the need to hack anything in the default ORFS installation. Like this:

if { [env_var_exists_and_non_empty PRE_CTS_TCL] } { source $::env(PRE_CTS_TCL) }

It would be nice, too, if every step in the flow supported a POST_STEP_TCL variable (only a few do currently).

Additional Context

No response

[maliberty]

These hooks have been added as the need arose. Feel free to make a PR with a more systematic treatment.