Fixes the following GCC 8 warnings:
```
core/object.h:321:32: warning: unnecessary parentheses in declaration of '_get_get' [-Wparentheses]
core/object.h:331:32: warning: unnecessary parentheses in declaration of '_get_set' [-Wparentheses]
core/object.h:341:32: warning: unnecessary parentheses in declaration of '_get_get_property_list' [-Wparentheses]
core/object.h:360:32: warning: unnecessary parentheses in declaration of '_get_notification' [-Wparentheses]
core/object.h:517:32: warning: unnecessary parentheses in declaration of '_get_get' [-Wparentheses]
core/object.h:520:32: warning: unnecessary parentheses in declaration of '_get_set' [-Wparentheses]
core/object.h:523:32: warning: unnecessary parentheses in declaration of '_get_get_property_list' [-Wparentheses]
core/object.h:526:32: warning: unnecessary parentheses in declaration of '_get_notification' [-Wparentheses]
```
Image::load is now issuing warnings (since ef50957) to prevent users
from using it to load images at runtime which would be included in
their exported game.
So we now use ImageLoader explicitly instead for the custom-handled
cases in Main.
Fixes#21072, supersedes #22321.
Fix for incorrect types used in MeshDataTool for bones and weights.
If your mesh contains these memory accesses get OOB and might crash
the application
Closes#21713
Fixes the following GCC 5 warnings:
```
core/io/zip_io.h:128:26: warning: 'zlib_filefunc_def zipio_create_io_from_file(FileAccess**)' defined but not used [-Wunused-function]
core/script_debugger_remote.cpp:110:17: warning: 'ObjectID safe_get_instance_id(const Variant&)' defined but not used [-Wunused-function]
drivers/unix/socket_helpers.h:103:12: warning: 'int _socket_create(IP::Type&, int, int)' defined but not used [-Wunused-function]
drivers/unix/socket_helpers.h:45:15: warning: 'size_t _set_sockaddr(sockaddr_storage*, const IP_Address&, int, IP::Type)' defined but not used [-Wunused-function]
drivers/unix/socket_helpers.h:76:15: warning: 'size_t _set_listen_sockaddr(sockaddr_storage*, int, IP::Type, IP_Address)' defined but not used [-Wunused-function]
editor/editor_fonts.cpp:40:24: warning: 'Ref<BitmapFont> make_font(int, int, int, int, const int*, const Ref<Texture>&)' defined but not used [-Wunused-function]
editor/editor_themes.cpp:85:26: warning: 'Ref<StyleBoxFlat> change_border_color(Ref<StyleBoxFlat>, Color)' defined but not used [-Wunused-function]
editor/import/editor_import_collada.cpp:493:13: warning: 'void _generate_normals(const PoolVector<int>&, const PoolVector<Vector3>&, PoolVector<Vector3>&)' defined but not used [-Wunused-function]
editor/import/editor_import_collada.cpp:524:13: warning: 'void _generate_tangents_and_binormals(const PoolVector<int>&, const PoolVector<Vector3>&, const PoolVector<Vector3>&, const PoolVector<Vector3>&, PoolVector<float>&)' defined but not used [-Wunused-function]
editor/pvrtc_compress.cpp:118:13: warning: 'void _compress_etc(Image*)' defined but not used [-Wunused-function]
modules/etc/image_etc.cpp:89:13: warning: 'void _decompress_etc1(Image*)' defined but not used [-Wunused-function]
modules/etc/image_etc.cpp:93:13: warning: 'void _decompress_etc2(Image*)' defined but not used [-Wunused-function]
modules/gdscript/editor/gdscript_highlighter.cpp:46:13: warning: 'bool _is_whitespace(CharType)' defined but not used [-Wunused-function]
scene/2d/cpu_particles_2d.cpp:510:14: warning: 'float rand_from_seed_m1_p1(uint32_t&)' defined but not used [-Wunused-function]
scene/3d/cpu_particles.cpp:474:14: warning: 'float rand_from_seed_m1_p1(uint32_t&)' defined but not used [-Wunused-function]
scene/resources/default_theme/default_theme.cpp:123:20: warning: 'Ref<Shader> make_shader(const char*, const char*, const char*)' defined but not used [-Wunused-function]
scene/resources/default_theme/default_theme.cpp:130:24: warning: 'Ref<BitmapFont> make_font(int, int, int, int, const int*, const Ref<Texture>&)' defined but not used [-Wunused-function]
```
Had to split `core/io/zip_io.h` into header and .cpp file without 'static' keyword.
Not fixed yet (static definition in header used in some files but not all):
```
modules/websocket/lws_helper.h:111:13: warning: 'void _lws_make_protocols(void*, int (*)(lws*, lws_callback_reasons, void*, void*, size_t), PoolVector<String>, _LWSRef**)' defined but not used [-Wunused-function]
```
Also fixed a couple other warnings missed in previous commits.
