perf(module:steps): do not run change detection if there are no nzIndexChange listeners

[arturovt]

PR Checklist

• 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

[x] Refactoring (no functional changes, no api changes)

[ ] Yes
[x] No

[zorro-bot]

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[codecov]

Codecov Report

Merging #7183 (72bb628) into master (77db914) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #7183      +/-   ##
==========================================
- Coverage   91.67%   91.66%   -0.01%     
==========================================
  Files         486      486              
  Lines       15868    15867       -1     
  Branches     2587     2586       -1     
==========================================
- Hits        14547    14545       -2     
- Misses       1007     1008       +1     
  Partials      314      314              

Impacted Files	Coverage Δ
components/steps/step.component.ts	96.00% <100.00%> (+0.08%)	⬆️
components/steps/steps.component.ts	94.80% <100.00%> (-0.14%)	⬇️
components/core/util/text-measure.ts	92.10% <0.00%> (-0.88%)	⬇️

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[hsuanxyz]

LGTM