Token amendment: text / code

## Tokens to amend

text / code / inline
text / code / block

## Context

Currently, both styles above are of font-size 16, with different line-height. I think we will need these also in size small and x-small. For instance, in the code diff component canonical/ds25#146 , I'd like the dev to decide which font size to use based on its context when consuming the component.

Start by reviewing the existing text, code, inline, and block token definitions, then read the code diff component context referenced by canonical/ds25#146. Compare the current 16px styles and their line-heights, and clarify which small and x-small variants are needed for each context. Done means the token options and the component’s context-specific font-size choice are agreed.

Written by the indexing model from the issue text.