feat: add font variables for components in theme v2

[MartinCupela]

Motivation
Consistency + possibility to change the font easily without having to write long selectors to override the default font settings for components. It seems that font rules is one of few that does not have its component variables.

Example

In order to change the textarea font we have to do the following:

.str-chat__message-input .str-chat__message-textarea-container .str-chat__message-textarea {
    font: var(--str-chat__body-text);
}

Easier would be something like:

.str-chat {
  --str-chat__message-input-textarea-font: var(--str-chat__body-text);
}

[szuperaz]

If you use CSS cascade layers, you can just write .str-chat__message-textarea, but the issue makes sense regardless of that