Merge bitcoin/bitcoin#27064: system: use %LOCALAPPDATA% as default datadir on windows

84900ac34f6888b7a851d0a6a5885192155f865c doc: add release-notes-27064.md (Matthew Zipkin)
855dd8d592c951a2b3239867ffbf66bb8677d470 system: use %LOCALAPPDATA% as default datadir on windows (Matthew Zipkin)

Pull request description:

  Closes https://github.com/bitcoin/bitcoin/issues/2391

  This PR changes the default datadir location on Windows from `C:\Users\Username\AppData\Roaming\Bitcoin` to `C:\Users\Username\AppData\Local\Bitcoin`. This change only applies to fresh installs. To preserve backwards compatibility, on startup we check for the existence of `C:\Users\Username\AppData\Roaming\Bitcoin\chainstate` and if it is there, we continue using the "Roaming" directory as the default datadir location.

  [Note that in Windows 11 this change may be moot:](https://learn.microsoft.com/en-us/uwp/api/windows.storage.applicationdata.roamingfolder?view=winrt-22621)

  > Roaming data and settings is no longer supported as of Windows 11. The recommended replacement is [Azure App Service](https://learn.microsoft.com/en-us/azure/app-service/). Azure App Service is widely supported, well documented, reliable, and supports cross-platform/cross-ecosystem scenarios such as iOS, Android and web. Settings stored here no longer roam (as of Windows 11), but the settings store is still available.

ACKs for top commit:
  achow101:
    ACK 84900ac34f6888b7a851d0a6a5885192155f865c
  BenWestgate:
    crACK https://github.com/bitcoin/bitcoin/commit/84900ac34f6888b7a851d0a6a5885192155f865c
  hebasto:
    re-ACK 84900ac34f6888b7a851d0a6a5885192155f865c, only addressed feedback since my recent [review](https://github.com/bitcoin/bitcoin/pull/27064#pullrequestreview-2028718273).

Tree-SHA512: 807c6e89571287e2c8f4934229aec91ef28e7d0a675234acf1b7d085c24c7b73a08b6e345fbfc9038e6239187b6b69c08490ddaa1c057de5ea975c4a000bba42

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