feat(module:rate): support customize character

[stygian-desolator]

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?

[ ] Bugfix
[x] 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?

https://ant.design/components/rate-cn/#components-rate-demo-character-function

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[codecov]

Codecov Report

Merging #6787 (907d5d3) into master (1ec3f64) will decrease coverage by 0.30%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #6787      +/-   ##
==========================================
- Coverage   89.88%   89.58%   -0.31%     
==========================================
  Files         479      488       +9     
  Lines       15489    15779     +290     
  Branches     2522     2423      -99     
==========================================
+ Hits        13923    14135     +212     
- Misses        943     1004      +61     
- Partials      623      640      +17     

Impacted Files	Coverage Δ
components/rate/rate-item.component.ts	88.88% <ø> (+1.38%)	⬆️
components/rate/rate.component.ts	96.03% <ø> (ø)
components/core/config/config.service.ts	91.17% <0.00%> (-5.89%)	⬇️
components/steps/steps.component.ts	91.13% <0.00%> (-5.79%)	⬇️
components/popconfirm/popconfirm.ts	96.00% <0.00%> (-4.00%)	⬇️
...onents/table/src/addon/filter-trigger.component.ts	40.90% <0.00%> (-2.57%)	⬇️
components/steps/step.component.ts	95.91% <0.00%> (-1.81%)	⬇️
components/select/select.component.ts	87.22% <0.00%> (-0.05%)	⬇️
components/empty/config.ts	100.00% <0.00%> (ø)
components/message/base.ts	87.70% <0.00%> (ø)
... and 252 more

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[wzhudev]

LGTM