fix(module: input-item): fix input decimal point problem

[shuizhongxiong]

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
[x] Documentation content changes
[ ] Application (the showcase website) / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

InputItem type类型设置为money情况下，没有验证数字格式。

Issue Number: 618

What is the new behavior?

InputItem type类型设置为money情况下，只允许输入一个小数点且不能是首位。

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[codecov]

Codecov Report

Merging #794 (56feb56) into master (71fb188) will decrease coverage by 0.02%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #794      +/-   ##
==========================================
- Coverage   86.89%   86.86%   -0.03%     
==========================================
  Files         164      164              
  Lines        6677     6679       +2     
  Branches     1115     1116       +1     
==========================================
  Hits         5802     5802              
- Misses        428      429       +1     
- Partials      447      448       +1     

Impacted Files	Coverage Δ
.../input-item/custom-input/custom-input.component.ts	89.43% <0.00%> (-1.28%)	⬇️

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