Move interleave(...) to the llvm namespace

[MForster]

This is for fixing the master-next build. Making this change on the master branch keeps the diff on master-next small. See also pull requests #31089 and #31090.

Unfortunately this leads to quite a bit of reformatting. I've used clang-format in the places where horizontal alignment broke. There are no syntactic changes at the call sites other than adding llvm::.

[gribozavr]

@swift-ci Please test

[MForster]

Here is a diff that contains the additional change that will be needed: for master-next: master-next...MForster:llvm-interleave-master-next. I'm not submitting this as a pull request yet, because I'm unsure how well GitHub works with dependent pull requests.

[MForster]

The test failure on the Windows build bot is not related to this pull request. The machine is running out of disk space.

[eeckstein]

@MForster When I tried to build master-next locally I found that this change is causing build failures, because now two interleave functions are in the llvm namespace:

/Users/erik/proj/main-swift/swift/lib/Demangling/NodePrinter.cpp:710:5: error: call to 'interleave' is ambiguous
    llvm::interleave(
    ^~~~~~~~~~~~~~~~
/Users/erik/proj/main-swift/llvm-project/llvm/include/llvm/ADT/STLExtras.h:1700:13: note: candidate function [with ForwardIterator = swift::Demangle::Node *const *, UnaryFunctor = (lambda at /Users/erik/proj/main-swift/swift/lib/Demangling/NodePrinter.cpp:712:9), NullaryFunctor = (lambda at /Users/erik/proj/main-swift/swift/lib/Demangling/NodePrinter.cpp:732:9), $3 = void]
inline void interleave(ForwardIterator begin, ForwardIterator end,
            ^
/Users/erik/proj/main-swift/swift/include/swift/Basic/STLExtras.h:90:13: note: candidate function [with ForwardIterator = swift::Demangle::Node *const *, UnaryFunctor = (lambda at /Users/erik/proj/main-swift/swift/lib/Demangling/NodePrinter.cpp:712:9), NullaryFunctor = (lambda at /Users/erik/proj/main-swift/swift/lib/Demangling/NodePrinter.cpp:732:9)]
inline void interleave(ForwardIterator begin, ForwardIterator end,
            ^
1 error generated.

[MForster]

There is a corresponding change on master-next that removes the copy: #31090 7b34593.

[eeckstein]

I see. Thanks