Core: Ensure classes match their header filename

Also drop some unused files.

Renamed:
- `core/dvector.h` -> `pool_vector.h`
- `core/io/resource_import.h` -> `resource_importer.h`
- `core/sort.h` -> `sort_array.h`
- `core/string_db.h` -> `string_name.h`

Dropped:
- `core/allocators.h`
- `core/os/shell.h`
- `core/variant_construct_string.cpp`

editor/import/editor_import_plugin.h

@@ -31,7 +31,7 @@
 #ifndef EDITOR_IMPORT_PLUGIN_H
 #define EDITOR_IMPORT_PLUGIN_H
 
-#include "core/io/resource_import.h"
+#include "core/io/resource_importer.h"
 
 class EditorImportPlugin : public ResourceImporter {
 	GDCLASS(EditorImportPlugin, Reference)

editor/import/resource_importer_bitmask.h

@@ -32,7 +32,7 @@
 #define RESOURCE_IMPORTER_BITMASK_H
 
 #include "core/image.h"
-#include "core/io/resource_import.h"
+#include "core/io/resource_importer.h"
 
 class StreamBitMap;
 

editor/import/resource_importer_csv_translation.h

@@ -31,7 +31,7 @@
 #ifndef RESOURCEIMPORTERCSVTRANSLATION_H
 #define RESOURCEIMPORTERCSVTRANSLATION_H
 
-#include "core/io/resource_import.h"
+#include "core/io/resource_importer.h"
 
 class ResourceImporterCSVTranslation : public ResourceImporter {
 	GDCLASS(ResourceImporterCSVTranslation, ResourceImporter)

editor/import/resource_importer_image.h

@@ -32,7 +32,7 @@
 #define RESOURCE_IMPORTER_IMAGE_H
 
 #include "core/image.h"
-#include "core/io/resource_import.h"
+#include "core/io/resource_importer.h"
 
 class ResourceImporterImage : public ResourceImporter {
 	GDCLASS(ResourceImporterImage, ResourceImporter)

editor/import/resource_importer_layered_texture.h

@@ -32,7 +32,7 @@
 #define RESOURCE_IMPORTER_LAYERED_TEXTURE_H
 
 #include "core/image.h"
-#include "core/io/resource_import.h"
+#include "core/io/resource_importer.h"
 
 class StreamTexture;
 

editor/import/resource_importer_scene.h

@@ -31,7 +31,7 @@
 #ifndef RESOURCEIMPORTERSCENE_H
 #define RESOURCEIMPORTERSCENE_H
 
-#include "core/io/resource_import.h"
+#include "core/io/resource_importer.h"
 #include "scene/resources/animation.h"
 #include "scene/resources/mesh.h"
 #include "scene/resources/shape.h"

editor/import/resource_importer_texture.h

@@ -32,7 +32,7 @@
 #define RESOURCEIMPORTTEXTURE_H
 
 #include "core/image.h"
-#include "core/io/resource_import.h"
+#include "core/io/resource_importer.h"
 
 class StreamTexture;
 

editor/import/resource_importer_wav.h

@@ -31,7 +31,7 @@
 #ifndef RESOURCEIMPORTWAV_H
 #define RESOURCEIMPORTWAV_H
 
-#include "core/io/resource_import.h"
+#include "core/io/resource_importer.h"
 
 class ResourceImporterWAV : public ResourceImporter {
 	GDCLASS(ResourceImporterWAV, ResourceImporter)