Get rid of CanonPath::fromCwd

As discussed in the last Nix team meeting (2024-02-95), this method
doesn't belong because `CanonPath` is a virtual/ideal absolute path
format, not used in file systems beyond the native OS format for which a
"current working directory" is defined.

Progress towards #9205

src/libexpr/paths.cc

@@ -1,5 +1,4 @@
 #include "eval.hh"
-#include "fs-input-accessor.hh"
 
 namespace nix {
 
@@ -8,4 +7,9 @@ SourcePath EvalState::rootPath(CanonPath path)
     return {rootFS, std::move(path)};
 }
 
+SourcePath EvalState::rootPath(PathView path)
+{
+    return {rootFS, CanonPath(absPath(path))};
+}
+
 }