Port member default initialization from constructor to declaration (C++11)

[akien-mga]

Using clang-tidy's modernize-use-default-member-init check and
manual review of the changes, and some extra manual changes that
clang-tidy failed to do.

The changes were initially done by calling run-clang-tidy.py -fix with the provided config, and using the newly merged feature that gives us a compilation database (#32848). It's not perfect though, it made some bogus changes which led to compilation errors which I had to fix manually.

[akien-mga]

Alright, I went through all of core/ manually to move everything I could find to default initialization on declaration. clang-tidy only handled the cases ported to list initializers already, so there was a lot of manual work left.

Which also mean probably one or two PEBKACs that may result in a broken engine... we'll see :)

[akien-mga]

Marking as WIP again as it needs more testing, I spotted a few regressions:

• Some text is missing in the project manager (welp)

• Project manager crashes on exit with:

Thread 1 "godot-git" received signal SIGSEGV, Segmentation fault.
0x00000000045822bf in OS::print_error (this=0x0, p_function=0x58acd01 "unref", p_file=0x58acc80 "core/string_name.cpp", p_line=102, p_code=0x58acd07 "BUG!", p_rationale=0x58a21f0 "", p_type=Logger::ERR_ERROR)
    at core/os/os.cpp:120
120             _logger->log_error(p_function, p_file, p_line, p_code, p_rationale, p_type);
(gdb) bt
#0  0x00000000045822bf in OS::print_error (this=0x0, p_function=0x58acd01 "unref", p_file=0x58acc80 "core/string_name.cpp", p_line=102, p_code=0x58acd07 "BUG!", p_rationale=0x58a21f0 "", 
    p_type=Logger::ERR_ERROR) at core/os/os.cpp:120
#1  0x00000000044026e8 in _err_print_error (p_function=0x58acd01 "unref", p_file=0x58acc80 "core/string_name.cpp", p_line=102, p_error=0x58acd07 "BUG!", p_message=0x58a21f0 "", p_type=ERR_HANDLER_ERROR)
    at core/error_macros.cpp:81
#2  0x000000000440260f in _err_print_error (p_function=0x58acd01 "unref", p_file=0x58acc80 "core/string_name.cpp", p_line=102, p_error=0x58acd07 "BUG!", p_type=ERR_HANDLER_ERROR) at core/error_macros.cpp:72
#3  0x00000000044ac554 in StringName::unref (this=0x7f37cf0) at core/string_name.cpp:102
#4  0x00000000044adb88 in StringName::~StringName (this=0x7f37cf0, __in_chrg=<optimized out>) at core/string_name.cpp:392
#5  0x0000000002df8a7e in Map<StringName, EditorDebuggerServer* (*)(String const&), Comparator<StringName>, DefaultAllocator>::Element::~Element (this=0x7f37cc0, __in_chrg=<optimized out>) at ./core/map.h:50
#6  0x0000000002df8aad in memdelete_allocator<Map<StringName, EditorDebuggerServer* (*)(String const&), Comparator<StringName>, DefaultAllocator>::Element, DefaultAllocator> (p_class=0x7f37cc0)
    at ./core/os/memory.h:128
#7  0x0000000002df86a6 in Map<StringName, EditorDebuggerServer* (*)(String const&), Comparator<StringName>, DefaultAllocator>::_cleanup_tree (this=0x69fb620 <EditorDebuggerServer::protocols>, 
    p_element=0x7f37cc0) at ./core/map.h:496
#8  0x0000000002df8486 in Map<StringName, EditorDebuggerServer* (*)(String const&), Comparator<StringName>, DefaultAllocator>::clear (this=0x69fb620 <EditorDebuggerServer::protocols>) at ./core/map.h:651
#9  0x0000000002df90a8 in Map<StringName, EditorDebuggerServer* (*)(String const&), Comparator<StringName>, DefaultAllocator>::~Map (this=0x69fb620 <EditorDebuggerServer::protocols>, __in_chrg=<optimized out>)
    at ./core/map.h:671
#10 0x00007ffff779b867 in __run_exit_handlers () from /lib64/libc.so.6
#11 0x00007ffff779ba0a in exit () from /lib64/libc.so.6
#12 0x00007ffff7785ce1 in __libc_start_main () from /lib64/libc.so.6
#13 0x00000000019d158a in _start () at ../sysdeps/x86_64/start.S:120

[Xrayez]

Just to note, I've made some similar changes while developing some custom module in C++, and I've had linker errors related to undefined constructors, then after scons --clean which then forces full rebuild I managed to compile everything again (MSVC 14.2, Godot 3.2 branch).

[akien-mga]

Taking some notes for myself:

• Some text is missing in the project manager (welp)

Reverting changes to scene fixes it, so I'll have to dig in there for the regression.

• Project manager crashes on exit with:

After reverting all my changes... turns out it's a bug in the master branch and not this PR? 😿

[akien-mga]

Some text is missing in the project manager (welp)

I had removed too much stuff from the Label constructor by mistake, should now be fixed.

Project manager crashes on exit

Confirmed in the master branch, so it's not this PR. I opened #38729.

[akien-mga]

It seems to work well in my tests, so I'll merge. I'd still welcome a review by senior devs on the changes in core as my C++-fu is not the most extensive, but it should be fairly enough to fix any potential mistake that sneaked into this PR.