[stdlib] Update documentation of integer types (swiftlang#74973)

* [stdlib] Remove docs from default implementations

Customized docs were not removed:

  public static var isSigned: Bool
  public static var max: Self
  public static var min: Self
  public var description: String
  public var magnitude: Self
  public init<T: BinaryInteger>(_ source: T)
  public func distance(to other: Self) -> Int
  public func advanced(by n: Int) -> Self

* [stdlib] Remove unused docs for "unsafe" methods

* [stdlib] Remove inherited "ReportingOverflow" docs

* [stdlib] Remove inherited docs for operators

Customized docs were not removed.
(`+`, `-`, `*`, `+=`, `-=`, `*=`)

Non-inherited docs were not removed.
(`&+`, `&-`, `&+=`, `&-=`, `&*=`)

* [stdlib] Reattach doc comments to their APIs

Use `rstrip()` to remove the trailing newline.
<https://docs.python.org/3/library/stdtypes.html#str.rstrip>

* [stdlib] Remove inherited docs from integer types

* [stdlib] Remove FIXME(ABI) comments

* [stdlib] Remove unused docs for operators

* [stdlib] Update example code for `-=` and `*=`

* [stdlib] Update internal gyb comments

* [stdlib] Move docs to BinaryInteger overrides

* [stdlib] Remove unused gyb code

* [stdlib] Fix `&-` and `&*` examples

Author: benrimmington