Don't rewrite a search prefix when attempting a suggestion

[oalders]

Fixes #1265

• Add some aria roles to search form and search alert
• Fix suggestion handling when there's a search prefix

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.56%. Comparing base (ff103ca) to head (87a81c9).

Files with missing lines	Patch %	Lines
lib/MetaCPAN/Web/Controller/Search.pm	50.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3343      +/-   ##
==========================================
- Coverage   73.61%   73.56%   -0.06%     
==========================================
  Files          67       67              
  Lines        2354     2357       +3     
  Branches      333      334       +1     
==========================================
+ Hits         1733     1734       +1     
- Misses        497      498       +1     
- Partials      124      125       +1     

Files with missing lines	Coverage Δ
lib/MetaCPAN/Web/Controller/Search.pm	79.24% <50.00%> (-2.76%)	⬇️

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