Categorize the extension settings

[jdneo]

So far, the vscode-java extension has 82 settings (configurable under User section). And all of them are grouped in one section Java, which is not very user-friendly.

A good example is GitLens extension, which has several sub sections for its settings:

it's achieved by defining the group in package.json: https://github.com/gitkraken/vscode-gitlens/blob/7b5205412dc333b7bc744ca00011f73e3304cfa2/package.json#L225-L227

We can adopt this as well.

@rgrunber @fbricon One question: If we adopt this capability, will this break Theia?

[fbricon]

@benoitf does Theia support setting categories?

[jdneo]

I installed newest gitlens in Theia, though the settings are not displayed in different groups, but all settings can be displayed in flat style. Looks like it will not break Theia and we can adopt this capability in VS Code.