fix($theme-default): close dropdown on mouseout (fix #2227)

[Mister-Hope]

Summary

What kind of change does this PR introduce? (check at least one)

• Bugfix

If changing the UI of default theme, please provide the before/after screenshot:

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)

You have tested in the following browsers: (Providing a detailed version will be better.)

• Chrome
• Firefox
• Safari
• Edge
• IE

[billyyyyy3320]

LGTM

[meteorlxy]

LGTM

[acgotaku]

The PR cause you can not open Languages dropdown in mobile mode. Please check at https://vuepress.vuejs.org/ .Thank you!

[Mister-Hope]

The PR cause you can not open Languages dropdown in mobile mode. Please check at https://vuepress.vuejs.org/ .Thank you!

Reproduced on my dad's iPhone, sorry for that because I don't have an iPhone iPad or Mac, so I did not test it on safari. It seems that safari has it's different way to deal with pointer-events, not the same as recommanded. I will try to fix it at once.

[Mister-Hope]

I searched some forum and docs, and since safari has it's own behavior, it will be unpossible to solve this problem with css.

I will fix it by adding some listeners and functions to solve this problem.

[billyyyyy3320]

@acgotaku Oops, Nice Catch.

[acgotaku]

@newsbielt703 @Mister-Hope Thanks for your reply!

[Mister-Hope]

I fix this issue on PR #2339 , you can try it out. @acgotaku @newsbielt703 .