fix($theme-default): wrong algolia search route with base config

[SigureMo]

Summary

Fix #1929
Fix #1802

Fix algolia search route is not correct in the case that $site.base is not /.

For example, in my project documention, I search some keywords, it will route to https://www.xxx.com/$site.base/$size.base/path/to/page/#hash rather than https://www.xxx.com/$site.base/path/to/page/#hash, $site.base is repeat.

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

• Bugfix
• Feature
• Code style update
• Refactor
• Docs
• Build-related changes
• Other, please describe:

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

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature
• Related documents have been updated
• Related tests have been updated

To avoid wasting your time, it's best to open a feature request issue first and wait for approval before working on it.

Other information:

[kefranabg]

Thanks @SigureMo, is the problem only occurring with algolia?

[SigureMo]

@kefranabg

Yes, default search does not have this problem. You can take a look at my another documention.

[haoranpb]

Is this going to solve #1802 as well?

[kefranabg]

Looks good 👍 One more approval to merge

[AaronCnvrg]

Would love to see this merged! Very important fix :)

[vue-bot]

Hey @SigureMo, thank you for your time and effort spent on this PR, contributions like yours help make Vue better for everyone. Cheers! 💚