Lots of tidying

- Removed generic `avr8` target
- Simplified AVR8 target construction
- Introduced register descriptor IDs
- Simplified GDB register mappings
- Simplified target interface contract
- Other bits of tidying

src/Services/TargetControllerService.cpp

@@ -159,9 +159,11 @@ namespace Bloom::Services
         );
     }
 
-    TargetRegisters TargetControllerService::readRegisters(const TargetRegisterDescriptors& descriptors) const {
+    TargetRegisters TargetControllerService::readRegisters(
+        const Targets::TargetRegisterDescriptorIds& descriptorIds
+    ) const {
         return this->commandManager.sendCommandAndWaitForResponse(
-            std::make_unique<ReadTargetRegisters>(descriptors),
+            std::make_unique<ReadTargetRegisters>(descriptorIds),
             this->defaultTimeout
         )->registers;
     }

src/Services/TargetControllerService.hpp

@@ -98,12 +98,12 @@ namespace Bloom::Services
         /**
          * Requests the TargetController to read register values from the target.
          *
-         * @param descriptors
-         *  Descriptors of the registers to read.
+         * @param descriptorIds
+         *  Descriptor IDs of the registers to read.
          *
          * @return
          */
-        Targets::TargetRegisters readRegisters(const Targets::TargetRegisterDescriptors& descriptors) const;
+        Targets::TargetRegisters readRegisters(const Targets::TargetRegisterDescriptorIds& descriptorIds) const;
 
         /**
          * Requests the TargetController to write register values to the target.