v6: Vertically center the KeycapHint glyph

[trevor-scheer]

Summary

• The glyph inside a KeycapHint key (⌘, ⌃, ⌥, ⇧, ⏎, letters) sat slightly above center. Centering the line box wasn't enough by itself, since these glyphs carry more ink above the baseline than below it.
• The glyph now renders in its own span with a small translateY nudge, measured against each glyph's actual ink bounds rather than guessed. ⌃ needed the most help; the rest were already close.

Test plan

• Open GraphiQL, look at a keycap hint in the top bar (e.g. the ⌘ ⏎ run shortcut), and confirm the glyph is vertically centered on the key.
• In Storybook, view Primitives/KeycapHint (Single, ChordWithModifier, RunShortcut stories) in both dark and light theme and confirm centering holds across the different glyphs.

Refs: #4219

[changeset-bot]

🦋 Changeset detected

Latest commit: 0668118

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 8 packages

Name	Type
@graphiql/react	Patch
@graphiql/plugin-code-exporter	Patch
@graphiql/plugin-collections	Patch
@graphiql/plugin-doc-explorer	Patch
@graphiql/plugin-explorer	Patch
@graphiql/plugin-history	Patch
@graphiql/plugin-query-builder	Patch
graphiql	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR