Use GCC 9 in travis.

CryptoCore class to access to base crypto utils.

Fix few GCC9 warnings:

thirdparty/assimp/include/assimp/material.inl: In member function 'aiReturn aiMaterial::Get(const char*, unsigned int, unsigned int, aiColor3D&) const':
thirdparty/assimp/include/assimp/material.inl:176:33: error: implicitly-declared 'aiColor3D& aiColor3D::operator=(const aiColor3D&)' is deprecated [-Werror=deprecated-copy]
  176 |     pOut = aiColor3D(c.r,c.g,c.b);

modules/dds/texture_loader_dds.cpp:167:50: error: comparison of integer expressions of different signedness: 'uint32_t' {aka 'unsigned int'} and 'int' [-Werror=sign-compare]
  167 |  if (format_flags & DDPF_FOURCC && format_fourcc == PF_FOURCC("DXT1")) {
      |                                                  ^
[ 28%] modules/dds/texture_loader_dds.cpp:170:57: error: comparison of integer expressions of different signedness: 'uint32_t' {aka 'unsigned int'} and 'int' [-Werror=sign-compare]
  170 |  } else if (format_flags & DDPF_FOURCC && format_fourcc == PF_FOURCC("DXT3")) {
      |                                                         ^
modules/dds/texture_loader_dds.cpp:174:57: error: comparison of integer expressions of different signedness: 'uint32_t' {aka 'unsigned int'} and 'int' [-Werror=sign-compare]
  174 |  } else if (format_flags & DDPF_FOURCC && format_fourcc == PF_FOURCC("DXT5")) {
      |                                                         ^
modules/dds/texture_loader_dds.cpp:177:57: error: comparison of integer expressions of different signedness: 'uint32_t' {aka 'unsigned int'} and 'int' [-Werror=sign-compare]
  177 |  } else if (format_flags & DDPF_FOURCC && format_fourcc == PF_FOURCC("ATI1")) {
      |                                                         ^
modules/dds/texture_loader_dds.cpp:180:57: error: comparison of integer expressions of different signedness: 'uint32_t' {aka 'unsigned int'} and 'int' [-Werror=sign-compare]
  180 |  } else if (format_flags & DDPF_FOURCC && format_fourcc == PF_FOURCC("ATI2")) {
      |                                                         ^
modules/dds/texture_loader_dds.cpp:183:57: error: comparison of integer expressions of different signedness: 'uint32_t' {aka 'unsigned int'} and 'int' [-Werror=sign-compare]
  183 |  } else if (format_flags & DDPF_FOURCC && format_fourcc == PF_FOURCC("A2XY")) {
      |                                                         ^

thirdparty/assimp/include/assimp/material.inl: In member function 'aiReturn aiMaterial::Get(const char*, unsigned int, unsigned int, aiColor3D&) const':
thirdparty/assimp/include/assimp/material.inl:176:33: error: implicitly-declared 'aiColor3D& aiColor3D::operator=(const aiColor3D&)' is deprecated [-Werror=deprecated-copy]
  176 |     pOut = aiColor3D(c.r,c.g,c.b);

It had been done wrongly in #30185, but I missed it.

Godot core needs MD5/SHA256/AES/Base64 which used to be provided by
separate libraries.
Since we bundle mbedtls in most cases, and we can easily only include
the needed sources if we so desire, let's use it.

To simplify library changes in the future, and better isolate header
dependencies all functions have been wrapped around inside a class in
`core/math/crypto_base.h`.

If the mbedtls module is disabled, we only bundle the needed source
files independently of the `builtin_mbedtls` option.
If the module is enabled, the `builtin_mbedtls` option works as usual.

Also remove some unused headers from StreamPeerMbedTLS which were
causing build issues.

Add a Direction property to ParticlesMaterial

Add editor screenshot on control - f12.

Remove thread to prevent memory leak

Add XR mode selection to the Android export process.

Expand/collapse nodes recursively in scene tree dock

New contributor added to AUTHORS:
@aqnuep

Thanks to all contributors and donors for making Godot possible!

Add buttons to remove keys\items from dictionaries\arrays.

SceneTreeDock will now only attach scripts to the selected node if the ScriptCreateDialog was opened from the SceneTreeDock

add 2d physic optimization similar to 3d physics

Keep GDScript functions in stack while yielding

Improve bookmarks

fixed an issue with double clicking available node in VisualScriptEditor 

Scale vertex lit lights by environment scale

Fix some editor crashes

Remove unnecessary code and add some error explanations

Revert "Add godot version in backtrace message"

Add 'global_rate_scale' to the AudioServer

Fix Emscripten root directory detection when building for HTML5

Fix TextEdit Select crash

Fix Nintendo buttons in the @GlobalScope documentation

Tweak gamepad button names to be consistent with the documentation

These were mistakenly referred to as DualShock buttons.