input: Allow configuring the completion popover max width

[narma]

Summary

The LSP completion popover width is currently capped at a hardcoded MAX_MENU_WIDTH of 320 px, and there's no public API to override it from outside the crate. That's fine for most identifiers, but it truncates longer LSP labels — e.g. database table identifiers like tbl_verification_tracking that show up in completions for editors hosting SQL/MongoDB/etc. clients.

This PR keeps the default at 320 px (no visual change for existing callers) and adds a way to widen the popover per editor:

• Renames the hardcoded MAX_MENU_WIDTH to DEFAULT_MAX_MENU_WIDTH (still pub(crate)).
• Stores max_width: Pixels on CompletionMenu and threads it through CompletionMenu::new, the items column, the documentation panel, and the side-by-side vs vertical layout overflow check.
• Adds two public methods on InputState:
  • completion_menu_max_width(width: Pixels) -> Self — builder.
  • set_completion_menu_max_width(width, window, cx) — runtime setter that also forwards into an already-open popover.

Usage:

InputState::new(window, cx)
    .code_editor("sql")
    .completion_menu_max_width(px(480.))

AI Assistance

🤖 The patch was drafted by Claude and reviewed/tested by a human; it follows the existing builder-method pattern used for placeholder, searchable, folding, etc.

Test plan

• cargo check -p gpui-component
• cargo clippy -p gpui-component -- -D warnings
• rustfmt on the three touched files
• Manual: open an editor with long completion labels, verify the popover caps at the configured width and still shrinks to fit when near the right viewport edge.
• Manual: confirm default behavior (no builder call) is unchanged at 320 px.

[huacnlee]

This is not a good API, but I don't know is there have a better choice.

[narma]

@huacnlee good point — agreed the two InputState::*completion_menu_max_width* methods felt off. I pushed ca0e6450 that tries a different shape, would this work better?

Instead of a dedicated builder + runtime setter on InputState, the option lives as a public field on Lsp, next to the other LSP-related config (completion_provider, code_action_providers, …):

pub struct CompletionMenuOptions {
    pub max_width: Pixels, // default 320 px
}

pub struct Lsp {
    pub completion_provider: ...,
    pub code_action_providers: ...,
    pub completion_menu: CompletionMenuOptions,
    ...
}

Usage from the embedder side:

let mut state = InputState::new(window, cx).code_editor("sql");
state.lsp.completion_menu.max_width = px(480.);

What this buys us:

• One discoverable place for completion-popover knobs, matching the existing public-field pattern on Lsp — no new methods on InputState.
• No duplicated state: CompletionMenu doesn't carry its own max_width copy anymore; on render it just reads self.editor.read(cx).lsp.completion_menu.max_width. Runtime changes propagate through the normal entity update flow, so the dedicated runtime setter is gone too.
• Future per-popover options (height, padding, doc-panel toggles) can be added as fields on CompletionMenuOptions without growing the InputState API surface.

Net diff vs the previous revision: +31 / −60 lines. Happy to iterate further if you'd prefer a different shape (e.g. keeping it on InputState but as a single completion_menu_options field/builder, or making it a pub(crate) getter on the popover entity instead).