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/impls/liveness.rs

@@ -40,7 +40,7 @@ impl<'tcx> Analysis<'tcx> for MaybeLiveLocals {
         // No variables are live until we observe a use
     }
 
-    fn apply_statement_effect(
+    fn apply_primary_statement_effect(
         &mut self,
         state: &mut Self::Domain,
         statement: &mir::Statement<'tcx>,
@@ -49,7 +49,7 @@ impl<'tcx> Analysis<'tcx> for MaybeLiveLocals {
         TransferFunction(state).visit_statement(statement, location);
     }
 
-    fn apply_terminator_effect<'mir>(
+    fn apply_primary_terminator_effect<'mir>(
         &mut self,
         state: &mut Self::Domain,
         terminator: &'mir mir::Terminator<'tcx>,
@@ -232,7 +232,7 @@ impl<'a, 'tcx> Analysis<'tcx> for MaybeTransitiveLiveLocals<'a> {
         // No variables are live until we observe a use
     }
 
-    fn apply_statement_effect(
+    fn apply_primary_statement_effect(
         &mut self,
         state: &mut Self::Domain,
         statement: &mir::Statement<'tcx>,
@@ -268,7 +268,7 @@ impl<'a, 'tcx> Analysis<'tcx> for MaybeTransitiveLiveLocals<'a> {
         TransferFunction(state).visit_statement(statement, location);
     }
 
-    fn apply_terminator_effect<'mir>(
+    fn apply_primary_terminator_effect<'mir>(
         &mut self,
         state: &mut Self::Domain,
         terminator: &'mir mir::Terminator<'tcx>,