fix(types): type element lists as tag name strings

[cossssmin]

Closes #389

heightElements, widthElements, tableElements and nonVisualElements were typed as HTMLElement[], which caused two problems:

• in Node projects without the dom lib, index.d.ts didn't compile at all (Cannot find name 'HTMLElement')
• even with dom, the type was wrong: at runtime these are upper-case tag names like ['TABLE', 'TD', 'TH', 'IMG'], so something like juice.widthElements = ['IMG', 'VIDEO'] was a type error and needed a cast

They're now string[], with a short doc comment noting the names are upper-case (that's how Juice compares them).

To keep DOM types from sneaking back in, the TypeScript test now runs without the dom lib (lib: ["ES2022"], types: ["node"]) and with skipLibCheck: false. With the old types it failed with exactly the four errors from the issue. It also assigns and reads all four lists as strings.

Heads-up for anyone who worked around this with a cast like as unknown as HTMLElement[]: that cast is now a type error, just remove it.

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