Bug 1679375 - Creates a Store interface and implements a WeakStore

[brizental]

This creates a generic interface to be implemented by all our stores, which will be:

• The different persistent stores that will need to be implemented per platform
• A weak store that can be used by all platforms

The interface follows the store design described in Glean.js: Client-side storage for web extensions. Applying the suggestion of consolidating create/update into a single function and renaming read to get (just sounded nicer, IMO).

Although the functions and their proposed functionalities are basically the same as in the proposal, the function signatures deviate from it. That was necessary, because the signatures proposed did not take into account the fact that our stores may contain multi-level objects.

This PR contains only the WeakStore implementation, the store which will not persist data throughout application runs. This implementation could also be used in the future to serve as a mock implementation on the persistent store for tests as well.

Finally, it also contains a bit of housekeeping work, namely:

• Added generated files to eslintignore;
• Added some more properties to tsconfig;
• Have CircleCI refrain from running the size check job on main (it fails on main and ultimately is unnecessary there).

[brizental]

Build size report

Merging brizental#6 into main will:

• Increase the size of the browser build (npm run build:browser) by 0%.
• Increase the size of the Qt build (npm run build:qt) by 0%.

---

Build	Current size	New size	Size increase
browser	4.44K	4.44K	📈 0%
qt	3.39K	3.39K	📈 0%

[brizental]

Build size report

Merging brizental#6 into main will:

• Increase the size of the browser build (npm run build:browser) by 0%.
• Increase the size of the Qt build (npm run build:qt) by 0%.

---

Build	Current size	New size	Size increase
browser	4.75K	4.75K	📈 0%
qt	3.69K	3.69K	📈 0%

[Dexterp37]

r+wc!