Debloat the binary by using less AsRef arguments

Using `impl AsRef<str>` as the argument instead of `&str` makes it
possible to call the function with `&str`, `String` and other types
that implement `AsRef` trait.

The cost of it is that compiled binary contains mulitple versions of
the same function, one for each variant of types. If function contains
multiple generic `impl AsRef` arguments, the number of versions possibly
compiled into binary grows exponentially with the number of arguments.

Simple way to avoid it is to call `.as_ref()` on the caller side to
convert the argument to `&str`. In most cases even adding a `&` and
relying on `Deref` coercion is sufficient.

This patch changes many functions that accepted `impl AsRef<str>` and
`impl AsRef<Path>` to accept `&str` and `&Path` instead.

In some places `.clone()` calls are removed. Calling `.clone()` on
`String` and passing `String` to a function accepting `impl
AsRef<str>` is completely unnecessary as `&str` reference could be
passed instead. There is no clippy warning against it yet, but
changing argument type to `&str` allowed to find these cases.

The result of debloating is not impressive, several hundred kilobytes
are saved, which is about 3% of the `.so` binary, but the code is
cleaner too.

src/mimefactory.rs

@@ -1278,7 +1278,7 @@ async fn build_body_file(
 }
 
 fn build_selfavatar_file(context: &Context, path: &str) -> Result<String> {
-    let blob = BlobObject::from_path(context, path)?;
+    let blob = BlobObject::from_path(context, path.as_ref())?;
     let body = std::fs::read(blob.to_abs_path())?;
     let encoded_body = wrapped_base64_encode(&body);
     Ok(encoded_body)
@@ -1328,8 +1328,8 @@ fn encode_words(word: &str) -> String {
     encoded_words::encode(word, None, encoded_words::EncodingFlag::Shortest, None)
 }
 
-fn needs_encoding(to_check: impl AsRef<str>) -> bool {
-    !to_check.as_ref().chars().all(|c| {
+fn needs_encoding(to_check: &str) -> bool {
+    !to_check.chars().all(|c| {
         c.is_ascii_alphanumeric() || c == '-' || c == '_' || c == '.' || c == '~' || c == '%'
     })
 }