perf(theme:modal): perf code

[cipchk]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ng-alain/delon/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
[ ] 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

[ng-alain-bot]

Preview is ready!

[codecov]

Codecov Report

Merging #1671 (a112e33) into master (3d6e016) will decrease coverage by 0.02%.
The diff coverage is 87.50%.

❗ Current head a112e33 differs from pull request most recent head ac83b22. Consider uploading reports for the commit ac83b22 to get more accurate results

@@            Coverage Diff             @@
##           master    #1671      +/-   ##
==========================================
- Coverage   96.17%   96.16%   -0.02%     
==========================================
  Files         282      282              
  Lines        8758     8758              
  Branches     1649     1649              
==========================================
- Hits         8423     8422       -1     
- Misses        323      324       +1     
  Partials       12       12              

Files	Coverage Δ
packages/theme/src/services/modal/modal.helper.ts	89.28% <87.50%> (ø)

... and 1 file with indirect coverage changes