fix(canvas) Leave jsx text blocks as they are when rendering the canvas

[Rheeseyb]

Fixes #1414

Problem:
React stringifies the children of <option> elements by design (see facebook/react#13465). Since we were wrapping jsx text blocks in a fragment when rendering on the canvas, that meant all options would be displayed as [object Object]. I don't believe we had an explicit reason for doing this, other than the return type of the rendering function was React.ReactElement.

Fix:
Change the return type of those rendering functions to React.ReactChild, which is a union of ReactElement, string and number, so that for jsx text blocks we can just return the text as intended.

[github-actions]

Link to test editor
Scroll Canvas: 35.9ms (25.9-56.4ms) | Resize: 69.2ms (17.4-134.1ms) | Selection: 262.5ms (205.5-740.2ms) | Calc Pi: 35ms (33-44ms) | Empty Dispatch: 42.1ms (37.6-150.4ms) |