Add Dump functions to Check, Parse, and Lex (#4669)

- Provide `Check::Dump(context, arg)` and similar.
- gdb and lldb should do contextual lookup, and `call Dump(*this,
Lex::TokenIndex::Invalid)` has been tested with gdb.
- Since this is only for debug, keeps the functions fully separated from
code.
- Uses alwayslink to ensure objects are correctly linked, even though
there are no calls.
- `-Wno-missing-prototypes` is needed when we don't have forward
declarations.
- Code is not linked in opt builds, using `#ifndef NDEBUG`.
- This probably could be doing something in BUILD files with a
`select()`, but the `#ifndef` seemed easier.

This is based on #4620, but uses free functions instead of member
functions.

Co-authored-by: Dana Jansens <danakj@orodu.net>

---------

Co-authored-by: danakj <danakj@orodu.net>

toolchain/lex/tokenized_buffer.cpp

@@ -25,7 +25,7 @@ auto TokenizedBuffer::GetLine(TokenIndex token) const -> LineIndex {
 }
 
 auto TokenizedBuffer::GetLineNumber(TokenIndex token) const -> int {
-  return GetLineNumber(GetLine(token));
+  return GetLine(token).index + 1;
 }
 
 auto TokenizedBuffer::GetColumnNumber(TokenIndex token) const -> int {
@@ -162,10 +162,6 @@ auto TokenizedBuffer::IsRecoveryToken(TokenIndex token) const -> bool {
   return recovery_tokens_[token.index];
 }
 
-auto TokenizedBuffer::GetLineNumber(LineIndex line) const -> int {
-  return line.index + 1;
-}
-
 auto TokenizedBuffer::GetNextLine(LineIndex line) const -> LineIndex {
   LineIndex next(line.index + 1);
   CARBON_DCHECK(static_cast<size_t>(next.index) < line_infos_.size());
@@ -262,7 +258,7 @@ auto TokenizedBuffer::PrintToken(llvm::raw_ostream& output_stream,
       llvm::right_justify(
           llvm::formatv("'{0}'", token_info.kind().name()).str(),
           widths.kind + 2),
-      llvm::format_decimal(GetLineNumber(GetLine(token)), widths.line),
+      llvm::format_decimal(GetLineNumber(token), widths.line),
       llvm::format_decimal(GetColumnNumber(token), widths.column),
       llvm::format_decimal(GetIndentColumnNumber(line_index), widths.indent),
       token_text);