Use abbreviation "expr" instead of "expression" (#3375)

Part of switching to the [abbreviations we've decided to
use](https://docs.google.com/document/d/1RRYMm42osyqhI2LyjrjockYCutQ5dOf8Abu50kTrkX0/edit?resourcekey=0-kHyqOESbOHmzZphUbtLrTw#heading=h.pph7i5m5un7q).

I will rename files in a follow-up PR.

toolchain/parse/handle_pattern.cpp

@@ -78,7 +78,7 @@ static auto HandlePattern(Context& context, Context::PatternKind pattern_kind)
     // Use the `:` or `:!` for the root node.
     state.token = context.Consume();
     context.PushState(state);
-    context.PushStateForExpression(PrecedenceGroup::ForType());
+    context.PushStateForExpr(PrecedenceGroup::ForType());
   } else {
     on_error();
     return;