Consider aligning success criteria and working mode with Web Apps charter

[tidoust]

See review comment from Mozilla in https://lists.w3.org/Archives/Public/public-new-work/2022Feb/0008.html:

we note that this WG has APIs that are intended for implementation by browser engines, similar but adjacent to the Web Apps
WG. To that extent we suggest including the text from the latest Web Apps WG Charter draft the "Success Criteria" (Section 1.1 here
https://w3c.github.io/webappswg/charter/draft-charter-2021.html#scope) and the "Working mode" (Section 5 here https://w3c.github.io/webappswg/charter/draft-charter-2021.html#working-mode) into the Second Screen Working Group Charter.

Review comment arises late in the re-chartering process for the current (2022) round of re-chartering as updates to these sections would change expectations that group participants and other reviewers have agreed to. Raising it as an issue for next time.

[tidoust]

Looking into this again as the charter needs to be renewed.

The change to the "Success Criteria" section would be to add: "In order to advance to Candidate Recommendation and to add features after reaching Candidate Recommendation, each feature is expected to be supported by at least two implementations, which may be judged by factors including existing implementations, expressions of interest, and lack of opposition."

The suggested working mode says "support from two or more web platform implementers is required before a substantive change can be made to a specification".

These changes would be significant in the sense that the approach taken by the Second Screen Working Group towards introducing features has been less strict until now (apart from assessing lack of opposition). The requirements still need to be met for specs to transition to Proposed Recommendation.

[anssiko]

I recommend aligning with the Process doc for CR transition requirements: https://www.w3.org/2023/Process-20231103/#transition-cr