[INFRA] add 'subprocess' visual tests

[aibcmars]

cover #541

[aibcmars]

subprocess lanes

[aibcmars]

inner subprocess

[tbouffard]

@aibcmars for the subprocess with lanes, what do you think of using elements without icons?
This will avoid that changes in user task or timer event break the test.
I would use abstract task instead of human task and would remove the timer event: the test still covers inner subprocess and elements positioning within the lanes of the subprocess.

I can manage the change from my own.

[aibcmars]

@aibcmars for the subprocess with lanes, what do you think of elements without icons?
This will avoid that changes in user task or timer event break the test.
I would use abstract task instead of human task and would remove the timer event: the test still covers inner subprocess and elements positioning within the lanes of the subprocess.

I can manage the change from my own.

good idea 👍