Remove useMultiline and multiline recipe

[raineorshine]

Current Behavior

Currently single line thoughts and multiline thoughts use different line-heights:

Single line thought:

em/src/components/Thought.tsx

Lines 423 to 425 in 2f074c6

	/* Use line-height to vertically center the text and bullet. We cannot use padding since it messes up the selection. This needs to be overwritten on multiline elements. See ".child .editable" below. */
	/* must match value used in Editable useMultiline */
	lineHeight: '1.72',

Multiline thought:

em/src/recipes/multiline.ts

Line 7 in 2f074c6

lineHeight: 1.25,

This is expensive to maintain, both in terms of development effort and performance. It requires a complex hook with costly DOM measurement (https://github.com/cybersemics/em/blob/2f074c6714c4bf9e6d833d991b342a69a5dbd80c/src/components/Editable/useMultiline.ts). Since there is no event that is fired when a thought wraps, we essentially need to measure the DOM anytime anything that could affect the line-wrapping changes. (A similar strategy is still necessary to measure the height of the thoughts for the LayoutTree.) This has many edge cases and is highly error prone. I am still encountering edge cases that fail to update the line-height when needed (e.g. #2501).

Expected Behavior

Given the fragility that this architecture introduced, it is worth revisiting this problem and attempting to eliminate the single line thought line-height.

• All thoughts should use the same line height
• Remove useMultiline
• Remove the multiline recipe
• The click area should not change
• The position should not change
• Test across platforms
• Test across different font sizes
• Add snapshot tests as needed

[raineorshine]

line-height must be used in order for the caret to be placed at the offset nearest the tap. Since the line-height on single-line thoughts must be large in order to have the correct click area and the line-height on multiline thoughts must be small to have the correct spacing in between lines, it is not possible to unify.

Detecting multiline is still the best way to get the desired caret behavior and spacing.