[quant] Use PlaceholderObserver as default dynamic quant observer

[jerryzh168]

Stack from ghstack:

• [quant][graphmode][fx][eagermode] Support sigmoid/hardsigmoid/tanh in eager and fx graph mode #45539 [quant][graphmode][fx][eagermode] Support sigmoid/hardsigmoid/tanh in eager and fx graph mode
• [quant] Add FixedQParamsFakeQuantize module #45538 [quant] Add FixedQParamsFakeQuantize module
• [quant][graphmode][fx][fix] Fix observer insert logic for ops that inherits quantization parameters for input #45473 [quant][graphmode][fx][fix] Fix observer insert logic for ops that inherits quantization parameters for input
• [quant][graphmode][fx] Merge all quantization mode #45292 [quant][graphmode][fx] Merge all quantization mode
• [quant] Use PlaceholderObserver as default dynamic quant observer #45343 [quant] Use PlaceholderObserver as default dynamic quant observer

Summary:
Current default dynamic quant observer is not correct since we don't accumulate
min/max and we don't need to calculate qparams.

Test Plan:

Reviewers:

Subscribers:

Tasks:

Tags:

Differential Revision: D23933995

[supriyar]

You would have to probably update the tests as well.

[dr-ci]

💊 CI failures summary and remediations

As of commit 6e9abe7 (more details on the Dr. CI page):

---

Commit 6e9abe7 was recently pushed. Waiting for builds...

---

This comment was automatically generated by Dr. CI (expand for details).

Follow this link to opt-out of these comments for your Pull Requests.

Please report bugs/suggestions on the GitHub issue tracker or post in the (internal) Dr. CI Users group.

See how this bot performed.

This comment has been revised 75 times.

[facebook-github-bot]

This pull request has been merged in 9d5607f.