Transition SR tag_invoke to member functions

[isidorostsa]

P2300 has moved away from the tag_invoke design pattern, following the guidance in P2855. This PR removes tag_invoke support from the P2300 CPOs used by our senders. However, sender-adapter CPOs can remain tag_invoke-friendly since they provide an operator() that internally calls tag_invoke. For example, when_all_vector must drop support for tag_invoke(set_value_t...), but the when_all_vector algorithm itself can still be implemented as a CPO using operator() that calls tag_invoke(when_all_vector_t) under the hood.

At present, the non-stdexec implementation of senders will not be updated to work without tag_invoke.

[codacy-production]

Coverage summary from Codacy

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Coverage variation	Diff coverage
Report missing for ea93afb1	✅ 100.00%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (ea93afb)	Report Missing	Report Missing	Report Missing
Head commit (010d56c)	194788	164979	84.70%

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#6709)	1	1	100.00%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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[hkaiser]

@isidorostsa I think this can be closed now as #7123 was merged. Please reopen if you think that this PR has applicable changes beyond what's already on master now.