Fix breakpoint issues on Windows

[lionel-]

Addresses posit-dev/positron#11558

This fixes two issues:

• We were passing file URIs to normalizePath(). On Unix this is fine, it doesn't find the path on disk and so returns the input since mustWork is FALSE:

  normalizePath("file:///home/user/test.R", mustWork = FALSE)
  #> [1] "file:///home/user/test.R"

  But on Windows this produces paths like C:\Users\lione\Projects\dplyr\file:\C:\Users\lione\OneDrive\Desktop\test.R

  To fix this, we detect all URIs rather than just Ark ones.

• On Windows, Positron sends encoded file URIs via to the LSP server and via execute-request code locations which look like c%03 instead of C:. These URIs didn't match the ones we constructed from file paths in the DAP. To fix this, we now normalise the URIs coming from the LSP (did change events for breakpoint invalidation) and from execute requests (so cmd+enter may validate breakpoints).

  Ideally we'd sanitize all URIs at the DAP/LSP/Jupyter boundaries to a common encoding, but such a large change felt too risky at this point. We will be able to do this when we introduce the notion of a FileId.

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