Bump to v1.2.0

[sunjiahao1999]

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Motivation

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Modification

Please briefly describe what modification is made in this PR.

BC-breaking (Optional)

Does the modification introduce changes that break the back-compatibility of the downstream repos?
If so, please describe how it breaks the compatibility and how the downstream projects should modify their code to keep compatibility with this PR.

Use cases (Optional)

If this PR introduces a new feature, it is better to list some use cases here, and update the documentation.

Checklist

1. Pre-commit or other linting tools are used to fix the potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
3. If the modification has potential influence on downstream projects, this PR should be tested with downstream projects.
4. The documentation has been modified accordingly, like docstring or example tutorials.

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (12e2b7c) 46.79% compared to head (ef3fef9) 46.79%.

❗ Current head ef3fef9 differs from pull request most recent head 03b2b64. Consider uploading reports for the commit 03b2b64 to get more accurate results

Additional details and impacted files

@@           Coverage Diff            @@
##           dev-1.x    #2630   +/-   ##
========================================
  Coverage    46.79%   46.79%           
========================================
  Files          277      277           
  Lines        23472    23473    +1     
  Branches      3659     3659           
========================================
+ Hits         10983    10984    +1     
  Misses       11793    11793           
  Partials       696      696           

Flag	Coverage Δ
unittests	46.79% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
mmdet3d/__init__.py	100.00% <100.00%> (ø)
mmdet3d/version.py	61.53% <100.00%> (ø)
mmdet3d/visualization/local_visualizer.py	26.51% <100.00%> (+0.16%)	⬆️

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