[clang] [NFC] Factor out common parts of ArraySections into its own class (PR #89639)

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@@ -74,12 +74,12 @@ void use() {
   for (int i = 0; i < 10; ++i) {
     // FIXME: Once we have a new array-section type to represent OpenACC as
     // well, change this error message.
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NagyDonat wrote:

This FIXME was resolved by this commit, consider removing it in a trivial follow-up change.

https://github.com/llvm/llvm-project/pull/89639