refactor(module:cascader): refactor cascader

[fbchen]

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
[x] Feature
[x] 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: #399 #422

What is the new behavior?

Does this PR introduce a breaking change?

[x] Yes
[ ] No

Other information

[codecov]

Codecov Report

Merging #1140 into 0.7.0 will decrease coverage by 0.52%.
The diff coverage is 96.84%.

@@            Coverage Diff             @@
##            0.7.0    #1140      +/-   ##
==========================================
- Coverage   98.01%   97.48%   -0.53%     
==========================================
  Files         146      181      +35     
  Lines        5479     7089    +1610     
  Branches      663      913     +250     
==========================================
+ Hits         5370     6911    +1541     
- Misses          0       18      +18     
- Partials      109      160      +51

Impacted Files	Coverage Δ
components/cascader/nz-cascader.module.ts	100% <100%> (ø)
components/cascader/nz-cascader.component.ts	96.79% <96.79%> (ø)
components/message/nz-message.module.ts	100% <0%> (ø)
components/tooltip/nz-tooltip.directive.ts	90% <0%> (ø)
components/popover/nz-popover.module.ts	100% <0%> (ø)
components/tooltip/nz-tooltip.module.ts	100% <0%> (ø)
components/slider/nz-slider-step.component.ts	91.66% <0%> (ø)
.../auto-complete/nz-autocomplete-option.component.ts	95.55% <0%> (ø)
components/auto-complete/index.ts	100% <0%> (ø)
...auto-complete/nz-autocomplete-trigger.directive.ts	96.47% <0%> (ø)
... and 29 more

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