feat(module:breadcrumb): support indenpendent separator

[wzhudev]

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)
[x] 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

[zorro-bot]

This preview will be available after the AzureCI is passed.

[codecov]

Codecov Report

Merging #4713 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #4713      +/-   ##
==========================================
+ Coverage   93.18%   93.18%   +<.01%     
==========================================
  Files         501      502       +1     
  Lines       12750    12751       +1     
  Branches     1957     1957              
==========================================
+ Hits        11881    11882       +1     
  Misses        457      457              
  Partials      412      412

Impacted Files	Coverage Δ
components/breadcrumb/breadcrumb-item.component.ts	100% <ø> (ø)
components/breadcrumb/breadcrumb.module.ts	100% <ø> (ø)
...nents/breadcrumb/breadcrumb-separator.component.ts	100% <100%> (ø)
components/breadcrumb/breadcrumb.component.ts	84.78% <100%> (ø)

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[hsuanxyz]

@wendellhu95 Rebase 一下