[LLDB][GUI] Add Process Launch form

This patch adds a process launch form. Additionally, a LazyBoolean field
was implemented and numerous utility methods were added to various
fields to get the launch form working.

Differential Revision: https://reviews.llvm.org/D107869

lldb/include/lldb/Target/Target.h

@@ -122,7 +122,16 @@ class TargetProperties : public Properties {
 
   void SetRunArguments(const Args &args);
 
+  // Get the whole environment including the platform inherited environment and
+  // the target specific environment, excluding the unset environment variables.
   Environment GetEnvironment() const;
+  // Get the platform inherited environment, excluding the unset environment
+  // variables.
+  Environment GetInheritedEnvironment() const;
+  // Get the target specific environment only, without the platform inherited
+  // environment.
+  Environment GetTargetEnvironment() const;
+  // Set the target specific environment.
   void SetEnvironment(Environment env);
 
   bool GetSkipPrologue() const;