[Feature Request(runtime-core)]: Make custom render setElementText optional

[neko-para]

Currently, setElementText method is marked as necessary. However, it's quite common for desktop ui that cannot perform setText on widget. Instead, text would be a dedicate widget. As this method could be emulated via other methods, allowing it be optional would be helpful.

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<text> abc </text>

will results createElement, setElementText(abc)

<text> abc {1} </text>

will results createElement, createText(abc), insert, createText(1), insert

The latter one tries to add children to a text, while text is supposed to be the leaf. If I do want to properly implement the custom render options, I'll have to create a dedicate text node, and each element shall manage a possible text node. It is quite complex. Currently, I've hacked the jsxs in jsx-runtime to manually join the children if type is text, which isn't really a good choice.