[reorg] Move ICSL script out of BERT folder

[eric-haibin-lin]

Description

A step further to make the bert folder thinner. Also add test for the script.

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

Changes

• Feature1, tests, (and when applicable, API doc)
• Feature2, tests, (and when applicable, API doc)

Comments

• If this change is a backward incompatible change, why must this change be made.
• Interesting edge cases to note here

[codecov]

Codecov Report

Merging #1131 into master will increase coverage by 0.55%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1131      +/-   ##
==========================================
+ Coverage   87.76%   88.32%   +0.55%     
==========================================
  Files          67       67              
  Lines        6310     6310              
==========================================
+ Hits         5538     5573      +35     
+ Misses        772      737      -35

Impacted Files	Coverage Δ
src/gluonnlp/model/attention_cell.py	92.17% <0%> (+1.67%)	⬆️
src/gluonnlp/model/transformer.py	91.66% <0%> (+4.48%)	⬆️
src/gluonnlp/model/utils.py	77.69% <0%> (+6.92%)	⬆️
src/gluonnlp/model/seq2seq_encoder_decoder.py	80% <0%> (+30%)	⬆️

[mli]

Job PR-1131/1 is complete.
Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-1131/1/index.html

[mli]

Job PR-1131/3 is complete.
Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-1131/3/index.html

[mli]

Job PR-1131/2 is complete.
Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-1131/2/index.html

[mli]

Job PR-1131/4 is complete.
Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-1131/4/index.html

[mli]

Job PR-1131/5 is complete.
Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-1131/5/index.html

[mli]

Job PR-1131/6 is complete.
Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-1131/6/index.html