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

Attention: Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 73.44%. Comparing base (ba434b7) to head (a0b2f4d).

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   73.49%   73.44%   -0.06%     
==========================================
  Files          68       68              
  Lines        2388     2391       +3     
  Branches      335      336       +1     
==========================================
+ Hits         1755     1756       +1     
- Misses        507      508       +1     
- Partials      126      127       +1     

Files with missing lines	Coverage Δ
lib/MetaCPAN/Web/Controller/Search.pm	78.43% <50.00%> (-2.82%)	⬇️

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