Add all() method and tests

[maxwellgerber]

This is a reference PR for #813 that adds all(): Array<{ name: string, value: string }>

This PR adds ~50 bytes to the final bundle size, keeping dist/js.cookie.min.mjs just barely under the 800 byte limit when gzipped.

This PR also adds a testcase that uses an iframe to create a scenario in which the same cookie name is set multiple times, with different values.

Running "compare_size:files" (compare_size) task
   raw     gz Sizes                                                            
  4052   1439 dist/js.cookie.mjs                                               
  1560    778 dist/js.cookie.min.mjs                                           
  4806   1625 dist/js.cookie.js                                                
  1863    893 dist/js.cookie.min.js                                            

   raw     gz Compared to main @ ab3f67fc4fad88cdf07b258c08e4164e06bf7506      
  +577   +194 dist/js.cookie.mjs                                               
  +132    +51 dist/js.cookie.min.mjs                                           
  +617   +196 dist/js.cookie.js                                                
  +132    +54 dist/js.cookie.min.js  

[github-actions]

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