* remove unnecessary hashes around raw string literals
* remove unncessary literal `unwrap()`s
* remove panicking `unwrap()`
* remove unnecessary `unwrap()`
* use `[]` instead of `vec![]` where applicable
* remove (more) unnecessary explicit `into_iter()` calls
* remove redundant pattern matching
* don't cast to same type and constness
* do not `cfg(any(...` a single item
* remove needless pass by `&mut`
* prefer `or_default()` to `or_insert_with(T::default())`
* `filter_map()` better written as `filter()`
* incorrect `PartialOrd` impl on `Ord` type
* replace "slow zero-filled `Vec` initializations"
* remove redundant local bindings
* add required lifetime to associated constant
In most cases, either a &Bank or an Arc<Bank> is more proper.
- &Bank is used if the function only needs a momentary reference
- Arc<Bank> is used if the function needs its' own copy
This PR leaves several instances of &Arc<Bank> around; these instances
are situations where a clone may only happen conditionally.
The core/src/ directory is already pretty crowded, and moving these
items into the subdirectory more clearly identifies that they are tied
to banking_stage.