Add support for storage area onChanged event listeners

[pinn3]

Aside from the onChanged events on the storage namespace, each storage
area (sync, local and managed) have their own onChanged event. This
event is tied to the area and as such, it has a different callback
function signature that only provides an object mapping with the
relevant StorageChange(s).

References:
https://developer.chrome.com/apps/storage#type-StorageArea
https://chromium.googlesource.com/chromium/src/+/master/extensions/common/api/storage.json#152

[codecov]

Codecov Report

Base: 99.50% // Head: 99.57% // Increases project coverage by +0.07% 🎉

Coverage data is based on head (a784e56) compared to base (09d3829).
Patch coverage: 100.00% of modified lines in pull request are covered.

❗ Current head a784e56 differs from pull request most recent head d53db65. Consider uploading reports for the commit d53db65 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #129      +/-   ##
==========================================
+ Coverage   99.50%   99.57%   +0.07%     
==========================================
  Files          14       12       -2     
  Lines         201      237      +36     
  Branches       43       48       +5     
==========================================
+ Hits          200      236      +36     
  Misses          1        1              

Impacted Files	Coverage Δ
src/storage.js	100.00% <100.00%> (ø)
src/index.js	100.00% <0.00%> (ø)
src/runtime.js	100.00% <0.00%> (ø)
src/extension.js
src/downloads.js

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[pinn3]

Noticed just now that this seems to be a Chrome specific thing and does not work with Firefox extensions. Is this something that's still relevant for this project? Otherwise this PR can be closed

[clarkbw]

Noticed just now that this seems to be a Chrome specific thing and does not work with Firefox extensions. Is this something that's still relevant for this project? Otherwise this PR can be closed

While we don't have any decent way to categorize these differences I don't see a reason we can't implement Chrome or Firefox only APIs.

[cainaj]

Can someone look at this PR? Looking for the support this code would provide.

[clarkbw]

Can someone look at this PR? Looking for the support this code would provide.

rebasing but this likely requires a lot more attention