Improve Linux terminal keymap and context menu (#16845)

Follow-up https://github.com/zed-industries/zed/pull/16085 that fixes
the search deploy to be actually a part of the terminal-related
bindings.

Part of https://github.com/zed-industries/zed/issues/16839

Also 

* fixes few other bindings to use `shift` and avoid conflicts with the
existing key bindings.
* adds terminal inline assist to the context menu and makes both the
menu and the button to dynamically adjust to `assist.enabled` settings
change

It is still unclear to me, why certain labels for certain bindings are
wrong (it's still showing `ctrl-w` for closing the terminal tab, and
`shift-insert` instead of `ctrl-shift-v` for Paste, while Insert is near
and has a `ctrl-shift-c` binding shown) but at least the keys work now.

Release notes: 
- Improved Linux terminal keymap and context menu

crates/assistant/src/assistant.rs

@@ -26,7 +26,7 @@ pub use context_store::*;
 use feature_flags::FeatureFlagAppExt;
 use fs::Fs;
 use gpui::Context as _;
-use gpui::{actions, impl_actions, AppContext, Global, SharedString, UpdateGlobal};
+use gpui::{actions, AppContext, Global, SharedString, UpdateGlobal};
 use indexed_docs::IndexedDocsRegistry;
 pub(crate) use inline_assistant::*;
 use language_model::{
@@ -69,13 +69,6 @@ actions!(
 
 const DEFAULT_CONTEXT_LINES: usize = 50;
 
-#[derive(Clone, Default, Deserialize, PartialEq)]
-pub struct InlineAssist {
-    prompt: Option<String>,
-}
-
-impl_actions!(assistant, [InlineAssist]);
-
 #[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord, Hash, Serialize, Deserialize)]
 pub struct MessageId(clock::Lamport);