You have posted that:
----“ was told by HR that if I got rank 4 or 5 in the next appraisal, I would be asked to resign.”
No one including HR can ask employee to sign letter of resignation. It cam be termed as offence.
Company can issue order of termination.
-----“ Kindly note that PIP did not include any training/counselling either from HR or my supervisor.”
PIP policy of all companies invariable include training.
PIP ---Performance Improvement Plan----involves identifying training needs and fulfilling training needs by providing training.
“Pl note that my technical skills were appreciated as well.”
The supervisor write stupid comments and it is obvious he was vindictive, zealous………..unprofessional, and HR became a party.
------“ Pl note that my new Supervisor had absolutely no involvement in the daily Tasks.”
The one who had no involvement how can he appraise???
-----“ The Management had received positive feedback about me from my Architect “
“I received positive feedbacks from the Client on this project.”
All of those who were involved and had a stake appreciated the employee and the appreciated was sent to management above this supervisor.
Despite this supervisor who had no involvement but was vindictive, zealous, biased, adamant, recalcitrant, posted negative feedback and again HR became a party and extracted resignation.
If the witnesses are unshakeable you may seek legal opinion from your lawyer and charge the offenders by name.
You may proceed under expert advice of your lawyer.