linux: Implement local time zone support (#14610)

I decided to remove the GPUI APIs since `chrono` already provides this
functionality, and is already been used for this purpose in other parts
of the code (e.g.
[here](80402a6840/crates/zed/src/main.rs (L756))
or
[here](80402a6840/crates/ui/src/utils/format_distance.rs (L258)))

These usages end up calling the `time_format` crate, which takes in a
`UtcOffset`. It's probably cleaner to rewrite the crate to take in
`chrono` types, but that would require rewriting most of the code there.

Release Notes:

- linux: Use local time zone in chat and Git blame

crates/gpui/src/platform/linux/platform.rs

@@ -30,7 +30,6 @@ use filedescriptor::FileDescriptor;
 use flume::{Receiver, Sender};
 use futures::channel::oneshot;
 use parking_lot::Mutex;
-use time::UtcOffset;
 use util::ResultExt;
 use wayland_client::Connection;
 use wayland_protocols::wp::cursor_shape::v1::client::wp_cursor_shape_device_v1::Shape;
@@ -397,10 +396,6 @@ impl<P: LinuxClient + 'static> Platform for P {
 
     fn set_dock_menu(&self, menu: Vec<MenuItem>, keymap: &Keymap) {}
 
-    fn local_timezone(&self) -> UtcOffset {
-        UtcOffset::UTC
-    }
-
     fn path_for_auxiliary_executable(&self, name: &str) -> Result<PathBuf> {
         Err(anyhow::Error::msg(
             "Platform<LinuxPlatform>::path_for_auxiliary_executable is not implemented yet",