fix: Add back DecodeError::new (#1382)

* fix: Add back `DecodeError::new`

This function was meant for internal use only. Because of `doc(hidden)` it was publicly available and it is actually used by users. The prost 0.14.2 release broken some of the crate ecosystem. That release was yanked. To prevent more breakage, this PR adds the function back. This time as a public function that is documented to not be used.

The prost project intents to remove this function in the next breaking release.

* Apply suggestion from @LucioFranco

---------

Co-authored-by: Lucio Franco <luciofranco14@gmail.com>

Author: caspermeijn

prost/src/error.rs

@@ -1,6 +1,7 @@
 //! Protobuf encoding and decoding errors.
 
 use crate::encoding::WireType;
+use alloc::borrow::Cow;
 #[cfg(not(feature = "std"))]
 use alloc::boxed::Box;
 #[cfg(not(feature = "std"))]
@@ -30,9 +31,25 @@ struct Inner {
 }
 
 impl DecodeError {
+    /// Creates a new `DecodeError` with a 'best effort' root cause description.
+    ///
+    /// Meant to be used only by `Message` implementations.
+    #[deprecated(
+        since = "0.14.2",
+        note = "This function was meant for internal use only. Because of `doc(hidden)` it was publicly available and it is actually used by users. The prost project intents to remove this function in the next breaking release."
+    )]
+    #[cold]
+    #[doc(hidden)]
+    pub fn new(description: impl Into<Cow<'static, str>>) -> DecodeError {
+        DecodeErrorKind::Other {
+            description: description.into(),
+        }
+        .into()
+    }
+
     /// Creates a new `DecodeError` with a DecodeErrorKind::UnexpectedTypeUrl.
     ///
-    /// Meant to be used only by `prost_types::Any` implementation.
+    /// Must only be used by `prost_types::Any` implementation.
     #[doc(hidden)]
     #[cold]
     pub fn new_unexpected_type_url(
@@ -115,6 +132,8 @@ pub(crate) enum DecodeErrorKind {
     InvalidString,
     /// Unexpected type URL
     UnexpectedTypeUrl { actual: String, expected: String },
+    /// A textual description of a problem
+    Other { description: Cow<'static, str> },
 }
 
 impl fmt::Display for DecodeErrorKind {
@@ -141,6 +160,9 @@ impl fmt::Display for DecodeErrorKind {
             Self::UnexpectedTypeUrl { actual, expected } => {
                 write!(f, "unexpected type URL.type_url: expected type URL: \"{expected}\" (got: \"{actual}\")")
             }
+            Self::Other { description } => {
+                write!(f, "{description}")
+            }
         }
     }
 }