[lldb][NFC] Move various constructor definitions from .h to .cpp

I ran into issues with linking downstream language plugin to liblldb in
debug builds, hitting link time errors of form:

```
undefined reference to `vtable for  lldb_private::<Insert LLDB class here>'
```

Anchoring the vtable to the .cpp files resolved those issues.

Differential Revision: https://reviews.llvm.org/D147252

Author: River707

lldb/include/lldb/Expression/ExpressionVariable.h

@@ -29,8 +29,7 @@ class ExpressionVariable
 
   LLVMCastKind getKind() const { return m_kind; }
 
-  ExpressionVariable(LLVMCastKind kind) : m_flags(0), m_kind(kind) {}
-
+  ExpressionVariable(LLVMCastKind kind);
   virtual ~ExpressionVariable();
 
   std::optional<uint64_t> GetByteSize() { return m_frozen_sp->GetByteSize(); }
@@ -208,8 +207,7 @@ class PersistentExpressionState : public ExpressionVariableList {
 
   LLVMCastKind getKind() const { return m_kind; }
 
-  PersistentExpressionState(LLVMCastKind kind) : m_kind(kind) {}
-
+  PersistentExpressionState(LLVMCastKind kind);
   virtual ~PersistentExpressionState();
 
   virtual lldb::ExpressionVariableSP

lldb/include/lldb/Expression/Materializer.h

@@ -69,6 +69,7 @@ class Materializer {
 
   class PersistentVariableDelegate {
   public:
+    PersistentVariableDelegate();
     virtual ~PersistentVariableDelegate();
     virtual ConstString GetName() = 0;
     virtual void DidDematerialize(lldb::ExpressionVariableSP &variable) = 0;

lldb/include/lldb/Symbol/TypeSystem.h

@@ -77,6 +77,7 @@ class TypeSystem : public PluginInterface,
                    public std::enable_shared_from_this<TypeSystem> {
 public:
   // Constructors and Destructors
+  TypeSystem();
   ~TypeSystem() override;
 
   // LLVM RTTI support

lldb/source/Expression/ExpressionVariable.cpp

@@ -15,6 +15,8 @@
 
 using namespace lldb_private;
 
+ExpressionVariable::ExpressionVariable(LLVMCastKind kind)
+    : m_flags(0), m_kind(kind) {}
 ExpressionVariable::~ExpressionVariable() = default;
 
 uint8_t *ExpressionVariable::GetValueBytes() {
@@ -30,6 +32,8 @@ uint8_t *ExpressionVariable::GetValueBytes() {
   return nullptr;
 }
 
+PersistentExpressionState::PersistentExpressionState(LLVMCastKind kind)
+    : m_kind(kind) {}
 PersistentExpressionState::~PersistentExpressionState() = default;
 
 lldb::addr_t PersistentExpressionState::LookupSymbol(ConstString name) {

lldb/source/Expression/Materializer.cpp

@@ -1598,5 +1598,7 @@ void Materializer::Dematerializer::Wipe() {
   m_process_address = LLDB_INVALID_ADDRESS;
 }
 
+Materializer::PersistentVariableDelegate::PersistentVariableDelegate() =
+    default;
 Materializer::PersistentVariableDelegate::~PersistentVariableDelegate() =
     default;

lldb/source/Symbol/TypeSystem.cpp

@@ -36,6 +36,7 @@ size_t LanguageSet::Size() const { return bitvector.count(); }
 bool LanguageSet::Empty() const { return bitvector.none(); }
 bool LanguageSet::operator[](unsigned i) const { return bitvector[i]; }
 
+TypeSystem::TypeSystem() = default;
 TypeSystem::~TypeSystem() = default;
 
 static TypeSystemSP CreateInstanceHelper(lldb::LanguageType language,