This used to be part of rust-analyzer, but it was causing problems. When rust-analyzer crashed or was slow, any enter press would be delayed for several seconds or never happen at all:
https://github.com/rust-analyzer/rust-analyzer/issues/4052
If you want you can add a keybinding:
"Preferences: Open Keyboard Shortcuts (JSON)"
[{
"command": "rust-analyzer.onEnter",
"key": "enter",
"when": "editorTextFocus && !suggestWidgetVisible && editorLangId == rust && !vim.active || vim.mode == 'Insert' && editorTextFocus && !suggestWidgetVisible && editorLangId == rust"
}]