Allow hiding codeBlockTitle in 2.0

Is your feature request related to a problem?

I am testing out the 2.0 beta, and so far it is much easier to customize and style. 👏

But, I see that a code demo title has been added, and it does not use a BEM class, so it's difficult to hide. I'd like to not show that title, to keep the same behavior as before.

Describe the solution you'd like

Add a BEM-style class to the codeBlockTitle component, so that I can hide it with display: none.

Describe alternatives you've considered

Additional context

Also, after hiding it, I'm getting fuzzy top borders in the corners because of this style:

.codeBlockTitle_node_modules-\@docusaurus-theme-classic-lib-theme-CodeBlock-Content-styles-module + .codeBlockContent_node_modules-\@docusaurus-theme-classic-lib-theme-CodeBlock-Content-styles-module .codeBlock_node_modules-\@docusaurus-theme-classic-lib-theme-CodeBlock-Content-styles-module {
    border-top-left-radius: 0;
    border-top-right-radius: 0;
}