feat: add has function to createContext

[soleuniverse101]

This is about #18471.

I hope it's okay, I went ahead and implemented this before having an answer on the issue about if this is okay as a feature. If it's not, I understand if this PR has to be closed, it was pretty quick to do.

If this PR is accepted, I have a few comments :

• First of all, feel free to argue this but I don't think introducing this additional function is a breaking change since all previous uses of createContext should still work by disregarding the third function of the now triplet returned.
• I replaced every [get, set] pair by a [get, set, has] triplet to reflect the new API so that people can notice the existence of the new has function. I was wondering if this was too much noise since people should probably mainly use get/set, while the use of has would be more rare.
• I slightly altered the Context docs page to reflect the new signature, but I didn't include any example since it shouldn't be needed often.
• To test this, I altered the runtime-runes/samples/create-context and runtime-runes/samples/create-context-programmatic tests. Is this okay or should I add new separate tests ?
• Finally, I noticed that the documentation of createContext mentions since 5.40.0. I'm not sure if I should update that or not, given that while the function was introducted at that version, this new signature would be more recent. How should I proceed ?

PS : sorry for the length of this body

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[changeset-bot]

🦋 Changeset detected

Latest commit: 6d5508d

The changes in this PR will be included in the next version bump.

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