SSH Remoting: Add the ability to resolve file paths on the remote host (#18250)

Release Notes:

- N/A

crates/proto/proto/zed.proto

@@ -293,7 +293,10 @@ message Envelope {
 
         TryExec try_exec = 252;
         ReadTextFile read_text_file = 253;
-        ReadTextFileResponse read_text_file_response = 254; // current max
+        ReadTextFileResponse read_text_file_response = 254;
+
+        CheckFileExists check_file_exists = 255;
+        CheckFileExistsResponse check_file_exists_response = 256; // current max
     }
 
     reserved 158 to 161;
@@ -2574,3 +2577,13 @@ message TryExec {
 message TryExecResponse {
     string text = 1;
 }
+
+message CheckFileExists {
+    uint64 project_id = 1;
+    string path = 2;
+}
+
+message CheckFileExistsResponse {
+    bool exists = 1;
+    string path = 2;
+}

crates/proto/src/proto.rs

@@ -372,7 +372,9 @@ messages!(
     (ShellEnvResponse, Foreground),
     (TryExec, Foreground),
     (ReadTextFile, Foreground),
-    (ReadTextFileResponse, Foreground)
+    (ReadTextFileResponse, Foreground),
+    (CheckFileExists, Background),
+    (CheckFileExistsResponse, Background)
 );
 
 request_messages!(
@@ -501,6 +503,7 @@ request_messages!(
     (ShellEnv, ShellEnvResponse),
     (ReadTextFile, ReadTextFileResponse),
     (TryExec, Ack),
+    (CheckFileExists, CheckFileExistsResponse)
 );
 
 entity_messages!(
@@ -578,7 +581,8 @@ entity_messages!(
     WhichCommand,
     ShellEnv,
     TryExec,
-    ReadTextFile
+    ReadTextFile,
+    CheckFileExists,
 );
 
 entity_messages!(