Lint to suggest `.saturating_add/sub(x)` for `.checked_add/sub(x).unwrap_or(MAX/MIN)`

[sinkuu]

unsigned.checked_add(x).unwrap_or(unsigned::MAX)
 -> unsigned.saturating_add(x)
unsigned.checked_sub(x).unwrap_or(0)
 -> unsigned.saturating_sub(x)

Signed versions can also be linted if literals are used.

signed.checked_add(non_negative_literal).unwrap_or(signed::MAX)
 -> signed.saturating_add(x)
signed.checked_add(    negative_literal).unwrap_or(signed::MIN)
 -> signed.saturating_add(x)

signed.checked_sub(non_negative_literal).unwrap_or(signed::MIN)
 -> signed.saturating_sub(x)
signed.checked_sub(    negative_literal).unwrap_or(signed::MAX)
 -> signed.saturating_sub(x)