This PR introduces a canonical way to endow a type with an order
structure. The basic operations (`LE`, `LT`, `Min`, `Max`, and in later
PRs `BEq`, `Ord`, ...) and any higher-level property (a preorder, a
partial order, a linear order etc.) are then put in relation to `LE` as
necessary. The PR provides `IsLinearOrder` instances for many core types
and updates the signatures of some lemmas.
**BREAKING CHANGES:**
* The requirements of the `lt_of_le_of_lt`/`le_trans` lemmas for
`Vector`, `List` and `Array` are simplified. They now require an
`IsLinearOrder` instance. The new requirements are logically equivalent
to the old ones, but the `IsLinearOrder` instance is not automatically
inferred from the smaller typeclasses.
* Hypotheses of type `Std.Total (¬ · < · : α → α → Prop)` are replaced
with the equivalent class `Std.Asymm (· < · : α → α → Prop)`. Breakage
should be limited because there is now an instance that derives the
latter from the former.
* In `Init.Data.List.MinMax`, multiple theorem signatures are modified,
replacing explicit parameters for antisymmetry, totality, `min_ex_or`
etc. with corresponding instance parameters.
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