feat(module:modal): add nzModalContent directive

[hsuanxyz]

close #6065

DEPRECATED: Usage <ng-content></ng-content> is deprecated, use <ng-template nzModalContent></ng-template> to declare the contents of the modal.

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: #6065

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 #6081 (a78812c) into master (3204927) will decrease coverage by 0.07%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##           master    #6081      +/-   ##
==========================================
- Coverage   89.89%   89.81%   -0.08%     
==========================================
  Files         465      466       +1     
  Lines       14057    14209     +152     
  Branches     2311     2237      -74     
==========================================
+ Hits        12636    12762     +126     
- Misses        873      894      +21     
- Partials      548      553       +5     

Impacted Files	Coverage Δ
components/modal/modal.module.ts	100.00% <ø> (ø)
components/modal/modal-content.directive.ts	50.00% <50.00%> (ø)
components/modal/modal.component.ts	92.77% <83.33%> (-3.53%)	⬇️
components/table/src/table/tr-expand.directive.ts	25.00% <0.00%> (-25.00%)	⬇️
components/badge/ribbon.component.ts	30.00% <0.00%> (-7.50%)	⬇️
components/table/src/table-data.service.ts	78.46% <0.00%> (-6.16%)	⬇️
components/tree-select/tree-select.component.ts	90.17% <0.00%> (-3.39%)	⬇️
...omponents/table/src/cell/th-selection.component.ts	30.76% <0.00%> (-2.57%)	⬇️
components/table/src/addon/selection.component.ts	7.69% <0.00%> (-1.40%)	⬇️
... and 71 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 3204927...a78812c. Read the comment docs.