fix(router): correct modifier key

[yuheiy]

On most browsers alt key will affect the behavior when clicking the link.

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/angular/angular/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
[ ] angular.io application / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

router link ignores the alt key.

What is the new behavior?

Respect the behaviors of browsers.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

[atscott]

This seems accurate based on my own testing and relatively low risk. Can you update the commit message to be a little more descriptive? Could you also provide some more justification and research into what actually does usually happen when links are clicked when holding the alt key on several different browsers?

[atscott]

Setting review to "request changes" per #25504 (comment)

[yuheiy]

@atscott I’m really sorry, but I made a git mistake and lost your commit. Instead I worked from HEAD of master branch and created a new pull request. #38375

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