fix(docsearch-react): add aria-hidden to SearchIcon and add accessible label to SearchBox input

[hbuchel]

There are 2 main changes in this PR:

• Allows passing aria-hidden to the SearchIcon so it can be hidden to assistive tech users. The unlabelled SVG can be accessed by screenreaders and can also get caught by automated accessibility audits. Since it's decorative, we can safely hide it with aria-hidden="true" in <SearchBox /> and <SearchButton />
• Adds an accessible label, searchInputLabel, to the search form's input. Currently the <input /> is associated with a <label> that does not have an accessible label, only an unlabelled SVG as a child element. This PR adds accessibly hidden text within the <label>. I opted to use visually hidden text (using CSS to hide the text but still make it available for assistive tech users) for the label text because it's generally a better practice than reaching for aria-label.

Additionally, this PR:

• Updates test to check for the new label text and translation, as well as fixes some TS related linting errors in that file.
• Updates the related docs to show the new translation option for searchInputLabel

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🔨 Latest commit	7a710c4

[hbuchel]

It doesn't look like we're using container anywhere besides in the before/afterEach? So I removed them.

[shortcuts]

awesome, thanks a lot for taking the time to improve DocSearch

cc @francoischalifour

[francoischalifour]

Thank you @hbuchel!

Could you please slightly increase the bundle size thresholds?

 {
   "files": [
     {
       "path": "packages/docsearch-css/dist/style.css",
-       "maxSize": "3 kB"
+       "maxSize": "3.25 kB"
     },
     {
       "path": "packages/docsearch-react/dist/umd/index.js",
-       "maxSize": "22.80 kB"
+       "maxSize": "23 kB"
     },
     {
       "path": "packages/docsearch-js/dist/umd/index.js",
-       "maxSize": "30.70 kB"
+       "maxSize": "31 kB"
     }
   ]
 }

[hbuchel]

Thank you @hbuchel!

Could you please slightly increase the bundle size thresholds?

Updated, thanks!