RBS 3.10 backport todo list

[soutaro]

We have to-backport:3.10 label in PRs.

We will backport the PRs with the label. This issue is to keep track of PRs that is already backported to the 3.10 branch.

[soutaro]

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[soutaro]

• Merge pull request #2718 from ruby/ruby-4 #2738

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[soutaro]

#2730 backported

• Move Pathname to core from stdlib #2705

[soutaro]

Working on #2740:

• Remove deprecated methods in JSON #2366
• Remove reference to JSON.deep_const_get #2701

[soutaro]

Working on #2741:

• Run CI with "4.0.0-preview2" #2718
• Avoid overloading where arguments are identical #2559
• Update rubocop-on-rbs #2496
• Update FileUtils to v1.8.0 #2700

[soutaro]

Working on #2742:

• Update existing docs #2724
• Fix tests for rbs_skip_tests in ruby repo #2725
• Update v4_0_0_preview2 to v4.0.0-preview2 #2743
• Update RBS files for Ruby 4 #2731

[soutaro]

#2722 backported:

• Update rdoc to v6.16 #2721

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Working on #2747:

• Update cgi and cgi/escape type definitions #2728

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Working on #2748:

• Make assertions macro #2729

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Working on #2750:

• Fix nil size Enumerator test #2749

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Working on #2751:

• Update rdoc and comments #2733
• Bundler 4.0.1 #2737

[soutaro]

Backporting PR: #2754

• Delete debug print #2753

[soutaro]

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