Introduce a ContactId newtype

This makes the contact ID its own newtype instead of being a plain
u32.  The change purposefully does not yet try and reap any benefits
from this yet, instead aiming for a boring change that's easy to
review.  Only exception is the ToSql/FromSql as not doing that yet
would also have created churn in the database code and it is easier to
go straight for the right solution here.

src/location.rs

@@ -8,6 +8,7 @@ use quick_xml::events::{BytesEnd, BytesStart, BytesText};
 use crate::chat::{self, ChatId};
 use crate::config::Config;
 use crate::constants::{Viewtype, DC_CONTACT_ID_SELF};
+use crate::contact::ContactId;
 use crate::context::Context;
 use crate::dc_tools::time;
 use crate::events::EventType;
@@ -25,7 +26,7 @@ pub struct Location {
     pub longitude: f64,
     pub accuracy: f64,
     pub timestamp: i64,
-    pub contact_id: u32,
+    pub contact_id: ContactId,
     pub msg_id: u32,
     pub chat_id: ChatId,
     pub marker: Option<String>,
@@ -558,7 +559,7 @@ pub async fn set_msg_location_id(context: &Context, msg_id: MsgId, location_id:
 pub(crate) async fn save(
     context: &Context,
     chat_id: ChatId,
-    contact_id: u32,
+    contact_id: ContactId,
     locations: &[Location],
     independent: bool,
 ) -> Result<Option<u32>> {
@@ -585,12 +586,12 @@ pub(crate) async fn save(
             conn.prepare_cached("SELECT id FROM locations WHERE timestamp=? AND from_id=?")?;
         let mut stmt_insert = conn.prepare_cached(stmt_insert)?;
 
-        let exists = stmt_test.exists(paramsv![timestamp, contact_id as i32])?;
+        let exists = stmt_test.exists(paramsv![timestamp, contact_id])?;
 
         if independent || !exists {
             stmt_insert.execute(paramsv![
                 timestamp,
-                contact_id as i32,
+                contact_id,
                 chat_id,
                 latitude,
                 longitude,