Move trace banners to driver and trace intermediate state. (#2443)

Printing intermediate state should be helpful to be able to examine the input when debugging later steps.

Intermediate state is hard to trace from the individual libraries since they don't know whether `dump` is going to print the state, so this moves some trace logic into the driver which is better equipped to make the decision.

toolchain/parser/parser.cpp

@@ -433,8 +433,6 @@ auto Parser::Parse() -> void {
   // Traces state_stack_. This runs even in opt because it's low overhead.
   PrettyStackTraceParseState pretty_stack(this);
 
-  CARBON_VLOG() << "*** Parser::Parse Begin ***\n";
-
   PushState(ParserState::DeclarationLoop());
   while (!state_stack_.empty()) {
     switch (state_stack_.back().state) {
@@ -447,8 +445,6 @@ auto Parser::Parse() -> void {
   }
 
   AddLeafNode(ParseNodeKind::FileEnd(), *position_);
-
-  CARBON_VLOG() << "*** Parser::Parse End ***\n";
 }
 
 auto Parser::HandleBraceExpressionState() -> void {