fix: fix added popular network

[salimtb]

Explanation

What is the current state of things and why does it need to change?

The current #onAddNetwork behavior in NetworkEnablementController was inconsistent and didn't provide a good user experience:

• All newly added networks were automatically enabled, regardless of context
• The logic for determining "popular networks mode" required ALL popular networks to be enabled, which was impractical
• Users experienced unexpected network switching when adding popular networks in multi-network scenarios

What is the solution your changes offer and how does it work?

This PR implements a more intuitive network addition behavior:

1. Improved Popular Networks Detection: Changed from requiring "all popular networks enabled" to ">2 popular networks enabled", making the detection much more practical and user-friendly.

2. Context-Aware Network Addition:

   • If in popular networks mode (>2 popular networks enabled) AND adding a popular network → Keep current selection (add but don't enable the new network)
   • Otherwise → Switch to the newly added network (disable all others, enable the new one)

3. Key Benefits:

   • When users have multiple popular networks enabled and add another popular network, their current workflow isn't disrupted
   • When users add non-popular networks or add networks when not in "popular mode", they get the expected behavior of switching to the new network
   • The popular networks threshold (>2) is much more realistic than requiring all popular networks

Are there any changes whose purpose might not obvious to those unfamiliar with the domain?

• The method rename from #areAllPopularNetworksEnabled() to #isInPopularNetworksMode() reflects the conceptual shift from checking all networks to checking if the user is in a "popular networks" usage pattern
• The ">2" threshold was chosen because it indicates the user is actively using multiple popular networks (suggesting they prefer the multi-network mode) vs. having just 1-2 networks enabled

References

This change improves the user experience for network management in MetaMask by implementing more intuitive network addition behavior based on user context.

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed, highlighting breaking changes as necessary
• I've prepared draft p