fix(module:form): fix form init style miss & fix doc

[vthinkxie]

close #1170 close #1173

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/NG-ZORRO/ng-zorro-antd/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Application (the showcase website) / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[codecov]

Codecov Report

Merging #1174 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1174      +/-   ##
==========================================
+ Coverage   96.75%   96.75%   +<.01%     
==========================================
  Files         184      184              
  Lines        7583     7586       +3     
  Branches      990      991       +1     
==========================================
+ Hits         7337     7340       +3     
  Misses         56       56              
  Partials      190      190

Impacted Files	Coverage Δ
components/form/nz-form-control.component.ts	100% <100%> (ø)	⬆️

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