Rename files to use abbreviations (#3389)

Reflects these recent PRs:
* #3375 
* #3382

toolchain/check/handle_expr_statement.cpp

@@ -0,0 +1,29 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include "toolchain/check/context.h"
+#include "toolchain/check/convert.h"
+#include "toolchain/sem_ir/inst.h"
+
+namespace Carbon::Check {
+
+// TODO: Find a better home for this. We'll likely need it for more than just
+// expression statements.
+static auto HandleDiscardedExpr(Context& context, SemIR::InstId expr_id)
+    -> void {
+  // If we discard an initializing expression, convert it to a value or
+  // reference so that it has something to initialize.
+  auto expr = context.insts().Get(expr_id);
+  Convert(context, expr.parse_node(), expr_id,
+          {.kind = ConversionTarget::Discarded, .type_id = expr.type_id()});
+
+  // TODO: This will eventually need to do some "do not discard" analysis.
+}
+
+auto HandleExprStatement(Context& context, Parse::Node /*parse_node*/) -> bool {
+  HandleDiscardedExpr(context, context.node_stack().PopExpr());
+  return true;
+}
+
+}  // namespace Carbon::Check