Make `Base.checked_add` and friends public

[LilithHafner]

[nsajko]

They're already public in Base.Checked, which is itself public in Base. Are you saying Base.Checked.checked_add is too much to type?

[LilithHafner]

According to the literal definition of the Julia API, it would not be breaking to change Base's using Checked to import Checked which would not break the public Base.Checked or the public Base.Checked.checked_add. I'd like to extend the API to guarantee that Base will continue to define the symbol checked_add directly (e.g. via using Checked or using Checked: checked_add).

Automated tools (e.g. the REPL) will use the literal definition so we should make sure it's accurate. For example:

help?> Base.checked_add
  │ Warning
  │
  │  The following bindings may be internal; they may change or be
  │  removed in future versions:
  │
  │    •  Base.checked_add

  Base.checked_add(x, y)

  Calculates x+y, checking for overflow errors where applicable.

  The overflow protection may impose a perceptible performance penalty.

We should do this with all symbols exported into Base that are intended to be publicly accessible with Base.symbol.

[nsajko]

IMO Base.Checked.checked_add is fine. I don't see a reason to additionally support Base.checked_add.

[LilithHafner]

In that case, the docstring of checked_add should be changed to not use Base.checked_add.

[nsajko]

Actually, I agree with Lilith. I think it'd be better to keep the doc strings as-is, considering they've been this way for quite a long time, and just make the bindings public in Base.