fix(treesitter): set `@type.builtin` as italic

[igorlfs]

Hello,

styles.properties is set as {} in the default config, which is truthy in Lua. Therefore, to actually fall back to italic, users would have to set styles.properties to nil (which I'm assuming is unintended behavior).

Alternatively, @type.builtin could be italic by default.

[comfysage]

hi, great observation. could you - as you suggested - also set the default option for types to italic?

[igorlfs]

also set the default option for types to italic?

Done! I removed the O.styles.properties, not sure if keeping it makes much sense? Setting that to italic would obviously affect some other stuff.