feat: implement TestController refreshHandler API

[Ricbet]

Types

• 🎉 New Features

Background or solution

背景: 默认情况下 Testing 是没有提供刷新操作的，需要插件自己往 workbench.view.testing 贡献点上注册刷新按钮，但这会导致 UI 上的冲突（比如会出现俩刷新按钮）

所以在 TestController 提供了 refreshHandler 的 API 方法，一旦实现了该方法，那么就会在如图所示的地方只出现一个刷新按钮

Changelog

实现 TestController.refreshHandler API

[codecov]

Codecov Report

Base: 57.63% // Head: 57.62% // Decreases project coverage by -0.00% ⚠️

Coverage data is based on head (0fac67a) compared to base (e8756c1).
Patch coverage: 11.11% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1865      +/-   ##
==========================================
- Coverage   57.63%   57.62%   -0.01%     
==========================================
  Files        1284     1284              
  Lines       80389    80406      +17     
  Branches    16823    16827       +4     
==========================================
+ Hits        46332    46334       +2     
- Misses      30976    30988      +12     
- Partials     3081     3084       +3     

Flag	Coverage Δ
jsdom	52.38% <11.11%> (-0.01%)	⬇️
node	15.88% <0.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
packages/core-browser/src/contextkey/testing.ts	0.00% <0.00%> (ø)
...tension/src/hosted/api/vscode/ext.host.api.impl.ts	91.95% <0.00%> (ø)
.../extension/src/hosted/api/vscode/ext.host.tests.ts	6.03% <0.00%> (-0.10%)	⬇️
...ension/src/browser/vscode/api/main.thread.tests.ts	16.32% <21.42%> (-0.53%)	⬇️
packages/utils/src/strings.ts	39.47% <0.00%> (+0.21%)	⬆️

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[erha19]

@Ricbet 这个加点单侧吧，放到 2.22 上发了

[erha19]

Unit Test will be resolved by #1878.