[BUGFIX] Fix quantized_op + requantize + dequantize fuse

[bgawrych]

Description

Fix for fusing requantize and dequantize into quantized op when it's outputs have different data types:

                 /---> Quantizable op
 Input ---> FC -|
                 \---> Non quantizable op

Found while quantizing google_electra models

Also this PR fixes invalid layer name requested for calibration - occurs when input to quantize node is variable

Checklist

Essentials

• PR's title starts with a category (e.g. [BUGFIX], [MODEL], [TUTORIAL], [FEATURE], [DOC], etc)
• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage
• Code is well-documented

[mxnet-bot]

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[bgawrych]

@mxnet-bot run ci [centos-cpu, clang, windows-cpu]

[mxnet-bot]

Jenkins CI successfully triggered : [windows-cpu, centos-cpu, clang]

[bartekkuncer]

LGTM

[bgawrych]

@akarbown Can we merge this?

[akarbown]

@akarbown Can we merge this?

@bgawrych Merged. Thanks!