fix various code completion text edits

[Techatrix]

// selecting the "src" completion item will add another "/"
const foo = @import("src<cursor>/main.zig");

// Completion items for modules will contain invalid text edits.
// The observable behavior varies between editors.
const known_folders = @import("<cursor>");

// The "foo" completion items will contain invalid text edits.
// The observable behavior varies between editors.
const foo = 5;
const bar = foo(<cursor>);