Rollup merge of rust-lang#102860 - GuillaumeGomez:missing-docs-FileNameDisplayPreference, r=nagisa

Add missing documentation for FileNameDisplayPreference variants

Took me a while to find the information when I needed it so hopefully it should save some time for the next ones.

r? ``@thomcc``

Author: JohnTitor

compiler/rustc_span/src/lib.rs

@@ -298,7 +298,11 @@ impl From<PathBuf> for FileName {
 
 #[derive(Clone, Copy, Eq, PartialEq, Hash, Debug)]
 pub enum FileNameDisplayPreference {
+    /// Display the path after the application of rewrite rules provided via `--remap-path-prefix`.
+    /// This is appropriate for paths that get embedded into files produced by the compiler.
     Remapped,
+    /// Display the path before the application of rewrite rules provided via `--remap-path-prefix`.
+    /// This is appropriate for use in user-facing output (such as diagnostics).
     Local,
 }