[lexical-code] Bug Fix: Add global type declarations for Prism

[etrepum]

Description

When investigating #6731 (comment) it was reported that npm run ci-check failed locally due to a type error. It's unclear why this failure doesn't also happen in CI, but I was able to reproduce it locally. The root cause probably has something to do with @types/prismjs and how the CI installs things?

All this does is add some type annotations to make it pass.

Test plan

Before

$ npm run tsc

> @lexical/monorepo@0.18.0 tsc
> tsc

packages/lexical-code/src/CodeHighlighterPrism.ts:28:59 - error TS7017: Element implicitly has an 'any' type because type 'typeof globalThis' has no index signature.

28 export const Prism: typeof import('prismjs') = globalThis.Prism || window.Prism;
                                                             ~~~~~

packages/lexical-code/src/CodeHighlighterPrism.ts:28:75 - error TS2339: Property 'Prism' does not exist on type 'Window & typeof globalThis'.

28 export const Prism: typeof import('prismjs') = globalThis.Prism || window.Prism;
                                                                             ~~~~~


Found 2 errors in the same file, starting at: packages/lexical-code/src/CodeHighlighterPrism.ts:28

After

$ npm run tsc

> @lexical/monorepo@0.18.0 tsc
> tsc

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Comments	Updated (UTC)
lexical	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Oct 15, 2024 7:55pm
lexical-playground	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Oct 15, 2024 7:55pm

[github-actions]

size-limit report 📦

Path	Size
lexical - cjs	29.94 KB (0%)
lexical - esm	29.81 KB (0%)
@lexical/rich-text - cjs	38.54 KB (0%)
@lexical/rich-text - esm	31.61 KB (0%)
@lexical/plain-text - cjs	37.15 KB (0%)
@lexical/plain-text - esm	28.99 KB (0%)
@lexical/react - cjs	40.34 KB (0%)
@lexical/react - esm	33.08 KB (0%)