Rename some Analysis and ResultsVisitor methods.

The words "before" and "after" have an obvious temporal meaning, e.g.
`seek_before_primary_effect`,
`visit_statement_{before,after}_primary_effect`. But "before" is also
used to name the effect that occurs before the primary effect of a
statement/terminator; this is `Effect::Before`. This leads to the
confusing possibility of talking about things happening "before/after
the before event".

This commit removes this awkward overloading of "before" by renaming
`Effect::Before` as `Effect::Early`. It also renames some of the
`Analysis` and `ResultsVisitor` methods to be more consistent.

Here are the before and after names:

- `Effect::{Before,Primary}`              -> `Effect::{Early,Primary}`
- `apply_before_statement_effect`         -> `apply_early_statement_effect`
- `apply_statement_effect`                -> `apply_primary_statement_effect`
- `visit_statement_before_primary_effect` -> `visit_after_early_statement_effect`
- `visit_statement_after_primary_effect`  -> `visit_after_primary_statement_effect`

(And s/statement/terminator/ for all the terminator events.)

compiler/rustc_mir_dataflow/src/points.rs

@@ -125,7 +125,7 @@ where
     A: Analysis<'tcx, Domain = BitSet<N>>,
     N: Idx,
 {
-    fn visit_statement_after_primary_effect(
+    fn visit_after_primary_statement_effect(
         &mut self,
         _results: &mut Results<'tcx, A>,
         state: &A::Domain,
@@ -139,7 +139,7 @@ where
         });
     }
 
-    fn visit_terminator_after_primary_effect(
+    fn visit_after_primary_terminator_effect(
         &mut self,
         _results: &mut Results<'tcx, A>,
         state: &A::Domain,