Suggest indexing for `str::char_indices().skip_while(|(i, _)| *i < index)`

let string = "example:hello";
let index = 5;

let result = string
    .char_indices()
    .skip_while(|(i, _)| *i < index)
    .find_map(|(i, c)| if c == ':' { Some(i) } else { None });

assert_eq!(result, Some(7))

could be optimized to

let string = "example:hello";
let index = 5;

let result = string[index..]
    .char_indices()
    .find_map(|(i, c)| if c == ':' { Some(i) } else { None })
    .map(|i| i + index);

assert_eq!(result, Some(7))

Indexing operations are faster than skipping to a specific index.

Start with the Rust examples in the issue and determine how Clippy recognizes the char_indices().skip_while pattern. The work is done when a lint suggests slicing at the byte index and preserves the demonstrated result, with appropriate coverage added in the Clippy test suite.