Set TERM env variable inside the terminal (#22615)

Closes #17991 

Release Notes:

- Set the `TERM` environment variable inside the terminal

Currently the terminal inherits the `TERM` variable from the parent
process. However this can cause issues with programs that rely on this
variable to make sure certain features are present. For example not
supporting backspaces making the terminal almost unusable.

crates/terminal/src/terminal.rs

@@ -347,6 +347,7 @@ impl TerminalBuilder {
 
         env.insert("ZED_TERM".to_string(), "true".to_string());
         env.insert("TERM_PROGRAM".to_string(), "zed".to_string());
+        env.insert("TERM".to_string(), "alacritty".to_string());
         env.insert(
             "TERM_PROGRAM_VERSION".to_string(),
             release_channel::AppVersion::global(cx).to_string(),