Add styling attributes to Site Title, Site Description, and Post Title Blocks

[apeatling]

Is your feature request related to a problem? Please describe.
In our user testing of full site editing on WordPress.com, users regularly expected to be able to style their site title and description in the same way they can with headings and paragraphs. They primarily expect to be able to change the font size, text color, and alignment of these blocks, and express frustration when they do not see the same options.

Describe the solution you'd like
There are three core blocks, Site Title, Site Description, and Post Title that currently do not support font size, text color, and alignment options. I suggest adding these so that when these blocks are ready to be used in production, we can avoid further user frustration.

• Site Title has been merged and can be updated: Add Site Title block and required functionality. #17207
• Site Description hasn't yet been merged: Site Tagline Block #23788
• Post Title as a block is very rudimentary, but it does exist: Block Library: Add Post Content and Title Blocks. #18461

/cc @obenland

[mrfoxtalbot]

I am not sure if this the best place to comment but I have found a couple of issues with the title and description block that I think should be addressed.

Basically whenever HTML is added to them (via copy-paste or by adding a line break) the HTML will be rendered in the front end, like this:

[strarsis]

This would be great because in one theme I want to allow the user to make parts of the post titles bold/emphasized, so the theme can style these parts differently. Currently an ACF field/metabox has to be used which is less intuitive.

[Copons]

@apeatling I took the liberty of updating the PR desc to replace the Site Description PR number.
The old one was too stale, so I've opened a new one: #23788