clang: Enable -Weverything, fix all warnings

This change fixes the following warnings:

```
    -Wc++98-compat-extra-semi
    -Wc++98-compat-local-type-template-args
    -Wc++98-compat-pedantic
    -Wc++98-compat
    -Wcomma
    -Wdeprecated-copy-dtor
    -Wexit-time-destructors
    -Wextra-semi-stmt
    -Wextra-semi
    -Wfloat-conversion
    -Wfloat-equal
    -Wformat-nonliteral
    -Wglobal-constructors
    -Winconsistent-missing-destructor-override
    -Wnon-virtual-dtor
    -Wold-style-cast
    -Wpadded
    -Wreturn-std-move-in-c++11
    -Wshadow-field-in-constructor
    -Wshadow-uncaptured-local
    -Wshift-sign-overflow
    -Wsign-conversion
    -Wundef
    -Wunreachable-code-return
    -Wused-but-marked-unused
    -Wweak-vtables
    -Wzero-as-null-pointer-constant
```

include/dap/serialization.h

@@ -38,6 +38,8 @@ struct Field {
 // Methods that return a bool use this to indicate success.
 class Deserializer {
  public:
+  virtual ~Deserializer() = default;
+
   // deserialization methods for simple data types.
   // If the stored object is not of the correct type, then these function will
   // return false.
@@ -104,7 +106,7 @@ bool Deserializer::deserialize(dap::optional<T>* opt) const {
   T v;
   if (deserialize(&v)) {
     *opt = v;
-  };
+  }
   return true;
 }
 
@@ -132,6 +134,8 @@ class FieldSerializer;
 // Methods that return a bool use this to indicate success.
 class Serializer {
  public:
+  virtual ~Serializer() = default;
+
   // serialization methods for simple data types.
   virtual bool serialize(boolean) = 0;
   virtual bool serialize(integer) = 0;
@@ -215,6 +219,8 @@ class FieldSerializer {
   template <typename T>
   using IsSerializeFunc = std::is_convertible<T, SerializeFunc>;
 
+  virtual ~FieldSerializer() = default;
+
   // field() encodes a field to the struct object referenced by this Serializer.
   // The SerializeFunc will be called with a Serializer used to encode the
   // field's data.