[Measurement] Group operators into just two extensions

[ikesyo]

A follow up for #1349.

Once this is merged, I will sync the file with the overlay.

[ikesyo]

@swift-ci Please test

[alblue]

@swift-ci please test

[alblue]

Looks like the swift build is hosed at the moment:

/home/buildnode/jenkins/workspace/swift-corelibs-foundation-PR-Linux/swift/include/swift/Runtime/Config.h:109:39: note: expanded from macro 'SWIFT_CC_swift'
#define SWIFT_CC_swift __attribute__((swiftcall))
                                      ^
/home/buildnode/jenkins/workspace/swift-corelibs-foundation-PR-Linux/swift/unittests/runtime/Stdlib.cpp:89:1: warning: unknown attribute 'swiftcall' ignored [-Wunknown-attributes]
SWIFT_CC(swift) SWIFT_RUNTIME_STDLIB_INTERNAL
^

[ianpartridge]

@swift-ci please test