Handy methods for Type::Params $arg objects

[tobyink]

Relates to #173 and #172.

[codecov]

Codecov Report

❌ Patch coverage is 96.05263% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.47%. Comparing base (d678dca) to head (6cddeee).
⚠️ Report is 26 commits behind head on master.

Files with missing lines	Patch %	Lines
lib/Type/Params/Signature.pm	96.05%	0 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #182      +/-   ##
==========================================
+ Coverage   91.84%   92.47%   +0.62%     
==========================================
  Files          30       30              
  Lines        3815     4569     +754     
  Branches      950     1246     +296     
==========================================
+ Hits         3504     4225     +721     
- Misses         11       15       +4     
- Partials      300      329      +29     

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