Add lint for checking exceeding bitshifts #17713
auto merge of #18206 : hirschenberger/rust/issue-17713, r=thestinger

Add lint for checking exceeding bitshifts #17713

It also const-evaluates the shift width (RHS) to check more complex shifts like `1u8 << (4+5)`.
The lint-level is set to `Warn` but perhaps it must be `Deny` as in llvm exceeding bitshifts are undefined as @ben0x539 stated in #17713