fix: update Secret with non-latin1 UTF-8 string

[Senorsen]

(This is a new PR against the current refactored master)

This PR will fix #7411.

Currently, I implement the fix using a third-party library: js-base64, and its size seems okay (minified ~8kb without tree-shaking; total build size: original 251388kb -> after 251392kb, +4kb).

Another way is using the unescape and encodeURIComponent trick:

btoa(unescape(encodeURIComponent(s)))

However, considered unescape is deprecated, maybe we should avoid using it. Am I right?

[codecov]

Codecov Report

Merging #7477 (7822596) into master (5d1383e) will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #7477      +/-   ##
==========================================
+ Coverage   42.27%   42.29%   +0.01%     
==========================================
  Files         220      220              
  Lines       12123    12123              
  Branches      179      179              
==========================================
+ Hits         5125     5127       +2     
+ Misses       6714     6711       -3     
- Partials      284      285       +1     

[maciaszczykm]

/lgtm
/approve

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