Rework ASTDumper (#68438)

This PR refactors the ASTDumper to make it more structured, less mistake-prone, and more amenable to future changes. For example:

```cpp
  // Before:
  void visitUnresolvedDotExpr(UnresolvedDotExpr *E) {
    printCommon(E, "unresolved_dot_expr")
      << " field '" << E->getName() << "'";
    PrintWithColorRAII(OS, ExprModifierColor)
      << " function_ref=" << getFunctionRefKindStr(E->getFunctionRefKind());
    if (E->getBase()) {
      OS << '\n';
      printRec(E->getBase());
    }
    PrintWithColorRAII(OS, ParenthesisColor) << ')';
  }

  // After:
  void visitUnresolvedDotExpr(UnresolvedDotExpr *E, StringRef label) {
    printCommon(E, "unresolved_dot_expr", label);

    printFieldQuoted(E->getName(), "field");
    printField(E->getFunctionRefKind(), "function_ref", ExprModifierColor);

    if (E->getBase()) {
      printRec(E->getBase());
    }

    printFoot();
  }
```

* Values are printed through calls to base class methods, rather than direct access to the underlying `raw_ostream`.
    * These methods tend to reduce the chances of bugs like missing/extra spaces or newlines, too much/too little indentation, etc.
    * More values are quoted, and unprintable/non-ASCII characters in quoted values are escaped before printing.
* Infrastructure to label child nodes now exists.
    * Some weird breaks from the normal "style", like `PatternBindingDecl`'s original and processed initializers, have been brought into line.
* Some types that previously used ad-hoc dumping functions, like conformances and substitution maps, are now structured similarly to the dumper classes.
* I've fixed the odd dumping bug along the way. For example, distributed actors were only marked `actor`, not `distributed actor`.

This PR doesn't change the overall style of AST dumps; they're still pseudo-S-expressions. But the logic that implements this style is now isolated into a relatively small base class, making it feasible to introduce e.g. JSON dumping in the future.

Author: beccadax

include/swift/AST/Expr.h

@@ -1118,6 +1118,9 @@ class ObjectLiteralExpr final : public LiteralExpr {
 #include "swift/AST/TokenKinds.def"
   };
 
+  static StringRef
+  getLiteralKindPlainName(ObjectLiteralExpr::LiteralKind kind);
+
 private:
   ArgumentList *ArgList;
   SourceLoc PoundLoc;

include/swift/AST/StorageImpl.h

@@ -203,8 +203,6 @@ enum class ReadImplKind {
 };
 enum { NumReadImplKindBits = 4 };
 
-StringRef getReadImplKindName(ReadImplKind kind);
-
 /// How are simple write accesses implemented?
 enum class WriteImplKind {
   /// It's immutable.
@@ -231,8 +229,6 @@ enum class WriteImplKind {
 };
 enum { NumWriteImplKindBits = 4 };
 
-StringRef getWriteImplKindName(WriteImplKind kind);
-
 /// How are read-write accesses implemented?
 enum class ReadWriteImplKind {
   /// It's immutable.
@@ -258,8 +254,6 @@ enum class ReadWriteImplKind {
 };
 enum { NumReadWriteImplKindBits = 4 };
 
-StringRef getReadWriteImplKindName(ReadWriteImplKind kind);
-
 class StorageImplInfo {
   using IntType = uint16_t;
   static_assert(NumReadImplKindBits + NumWriteImplKindBits

include/swift/AST/TypeRepr.h

@@ -189,6 +189,7 @@ class alignas(1 << TypeReprAlignInBits) TypeRepr
   void print(raw_ostream &OS, const PrintOptions &Opts = PrintOptions()) const;
   void print(ASTPrinter &Printer, const PrintOptions &Opts) const;
   SWIFT_DEBUG_DUMP;
+  void dump(raw_ostream &OS, unsigned indent = 0) const;
 };
 
 /// A TypeRepr for a type with a syntax error.  Can be used both as a