[Support] [Path] Move function declarations to the right doxygen group in the header. NFC.

[mstorsjo]

Summary

They were in the doxygen group Observers, while they are about
mutating paths.

[thakis]

lgtm

llvm/include/llvm/Support/Path.h

 /// @param NewPrefix The path prefix to replace \a NewPrefix with.
 /// @param style The style used to match the prefix. Exact match using
 /// Posix style, case/separator insensitive match for Windows style.
 /// @result true if \a Path begins with OldPrefix
 bool replace_path_prefix(SmallVectorImpl<char> &Path, StringRef OldPrefix,
                          StringRef NewPrefix,
                          Style style = Style::native);
 
+/// Remove redundant leading "./" pieces and consecutive separators.
+///
+/// @param path Input path.
+/// @result The cleaned-up \a path.
+StringRef remove_leading_dotslash(StringRef path, Style style = Style::native);
+
+/// In-place remove any './' and optionally '../' components from a path.
+///
+/// @param path processed path
+/// @param remove_dot_dot specify if '../' (except for leading "../") should be
+/// removed
+/// @result True if path was changed
+bool remove_dots(SmallVectorImpl<char> &path, bool remove_dot_dot = false,
+                 Style style = Style::native);
+
 /// Append to path.
 ///
 /// @code
 ///   /foo  + bar/f => /foo/bar/f
 ///   /foo/ + bar/f => /foo/bar/f
 ///   foo   + bar/f => foo/bar/f
 /// @endcode
 ///

 bool is_absolute_gnu(const Twine &path, Style style = Style::native);
 
 /// Is path relative?
 ///
 /// @param path Input path.
 /// @result True if the path is relative, false if it is not.
 bool is_relative(const Twine &path, Style style = Style::native);
 
-/// Remove redundant leading "./" pieces and consecutive separators.
-///
-/// @param path Input path.
-/// @result The cleaned-up \a path.
-StringRef remove_leading_dotslash(StringRef path, Style style = Style::native);
-
-/// In-place remove any './' and optionally '../' components from a path.
-///
-/// @param path processed path
-/// @param remove_dot_dot specify if '../' (except for leading "../") should be
-/// removed
-/// @result True if path was changed
-bool remove_dots(SmallVectorImpl<char> &path, bool remove_dot_dot = false,
-                 Style style = Style::native);
-
 } // end namespace path
 } // end namespace sys
 } // end namespace llvm
 
 #endif