Godot-proposals: Improve output log / enable filtering for warnings, errors and verbose messages

[Flavelius]

Describe the project you are working on:
None

Describe the problem or limitation you are having in your project:
The output log gets spammed with messages that are irrelevant to regular users for certain interactions with the editor, but they prevent easily catching actual errors that get pushed out of sight this way.

Describe the feature / enhancement and how it helps to overcome the problem or limitation:
Adding an option to the output panel or editor settings that allows controlling the log types would help, like filter type toggles/mask or a log-type level dropdown.

Describe how your proposal will work, with code, pseudocode, mockups, and/or diagrams:
For example as type toggles:

or

where i'd personally prefer the latter

If this enhancement will not be used often, can it be worked around with a few lines of script?:
I don't think it can without diving deep.
Is there a reason why this should be core and not an add-on in the asset library?:
It's not a big change, but it improves working with the engine. It may be hackable with editorplugins but it's such a basic functionality that most users would not now exists if distributed via assetlibrary, as it's typically expected to be part of the editor (as in other engines)

[rileylyman]

I took a stab at this in the above PR. Let me know what you think.