Backport HMACContext to 3.x

[tavurth]

I backported this PR #43536

Thank you @jonbonazza!

I also tested with this simple script from the docs:

godotengine/godot-proposals#1098

extends Control

var ctx = HMACContext.new()

func _ready():
	var key = "supersecret".to_utf8()
	var err = ctx.start(HashingContext.HASH_SHA256, key)
	assert(err == OK)
	var msg1 = "this is ".to_utf8()
	var msg2 = "vewy vewy secret".to_utf8()
	err = ctx.update(msg1)
	assert(err == OK)
	err = ctx.update(msg2)
	assert(err == OK)
	var hmac = ctx.finish()
	print(hmac.hex_encode())

godotengine/godot-proposals#1127

[Faless]

The script you mention in the PR is not the one for HMAContext, but for AESContext (which was already backported).
The tests in main/tests/* cannot be run as they are not called in main_test.cpp and would not compile anyway due to missing references.
We can either skip those, or add the missing functions.

[tavurth]

Thank you for the review @Faless!

I've made the changes you requested, since those tests won't run anyway (/mbedtls/tests I couldn't figure out the dependency tree) I removed them for now.

I updated the PR description with the ammended HMAC test, sorry my mistake for that. I checked and it's working also.

I couldn't find how to run tests locally, is that documented anywhere?

[Faless]

I couldn't find how to run tests locally

bin/godot --test crypto

[tavurth]

Thank you!

                                                                                                                                                     15m ⚑
▶ ./bin/godot.osx.tools.x86_64 --test crypto
arguments
0: ./bin/godot.osx.tools.x86_64
1: --test
2: crypto
Current path: /Users/will/src/godot
Godot Engine v3.4.beta.custom_build.0f88bdc07 - https://godotengine.org
OpenGL ES 3.0 Renderer: Intel(R) Iris(TM) Plus Graphics 655
OpenGL ES Batching: ON

Registered camera FaceTime HD Camera (Built-in) with id 1 position 0 at index 0
	PASS

Passed 1 of 1 tests

[akien-mga]

Does the test pass when compiling with module_mbedtls_enabled=no?

[tavurth]

Good question, I compiled just now using:

scons platform=osx arch=x86_64 module_mbedtls_enabled=no --jobs=$(sysctl -n hw.logicalcpu)

And tests are passing, is that correct?

[Faless]

Looks good, thanks! 👍

[akien-mga]

Thanks! And congrats for your first merged Godot contribution 🎉

[tavurth]

Thank you @akien-mga @Faless!