fix(module:picker): fix picker wrap z-index same as mask

[Guoyuanqiang]

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-mobile/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
[ ] 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?

Does this PR introduce a breaking change?

[ ] Yes
[ ] No

Other information

[codecov]

Codecov Report

Merging #362 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #362   +/-   ##
=======================================
  Coverage   89.58%   89.58%           
=======================================
  Files         229      229           
  Lines        6891     6891           
  Branches      564      564           
=======================================
  Hits         6173     6173           
  Misses        554      554           
  Partials      164      164

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[Guoyuanqiang]

close #360