[Collapse] Add support for unitless collapsedHeight

[weslenng]

Closes #18435

• I have followed (at least) the PR section of the contributing guide.

[mui-pr-bot]

Details of bundle changes.

Comparing: 508f9a3...fa6a6af

bundle	Size Change	Size	Gzip Change	Gzip
@material-ui/lab	▲ +41 B (+0.02% )	172 kB	▲ +16 B (+0.03% )	51.9 kB
Collapse	▲ +41 B (+0.06% )	66.5 kB	▲ +16 B (+0.08% )	20.5 kB
ExpansionPanel	▲ +41 B (+0.06% )	69.9 kB	▲ +16 B (+0.07% )	21.8 kB
docs.main	▲ +41 B (+0.01% )	609 kB	▲ +15 B (+0.01% )	194 kB
@material-ui/core	▲ +41 B (+0.01% )	351 kB	▲ +14 B (+0.01% )	96 kB
TreeItem	▲ +41 B (+0.06% )	72.2 kB	▲ +14 B (+0.06% )	22.8 kB
StepContent	▲ +41 B (+0.06% )	67.6 kB	▲ +13 B (+0.06% )	21.1 kB
@material-ui/core[umd]	▲ +41 B (+0.01% )	310 kB	▲ +11 B (+0.01% )	89.3 kB
@material-ui/styles	--	50.8 kB	--	15.4 kB
@material-ui/system	--	14.8 kB	--	4.06 kB
AppBar	--	62.4 kB	--	19.5 kB
Autocomplete	--	126 kB	--	40 kB
Avatar	--	61.4 kB	--	19.3 kB
Backdrop	--	66.4 kB	--	20.5 kB
Badge	--	64 kB	--	19.8 kB
BottomNavigation	--	61 kB	--	19.1 kB
BottomNavigationAction	--	74 kB	--	23.4 kB
Box	--	69.4 kB	--	21 kB
Breadcrumbs	--	66.6 kB	--	20.9 kB
Button	--	78 kB	--	23.8 kB
ButtonBase	--	72.5 kB	--	22.7 kB
ButtonGroup	--	80.6 kB	--	24.7 kB
Card	--	61.3 kB	--	19.2 kB
CardActionArea	--	73.6 kB	--	23.2 kB
CardActions	--	60.7 kB	--	19 kB
CardContent	--	60.6 kB	--	18.9 kB
CardHeader	--	63.7 kB	--	20 kB
CardMedia	--	61 kB	--	19.1 kB
Checkbox	--	80.4 kB	--	25.2 kB
Chip	--	81.1 kB	--	24.8 kB
CircularProgress	--	62.7 kB	--	19.7 kB
ClickAwayListener	--	3.87 kB	--	1.56 kB
colorManipulator	--	3.83 kB	--	1.52 kB
Container	--	61.8 kB	--	19.3 kB
CssBaseline	--	56.2 kB	--	17.6 kB
Dialog	--	81.2 kB	--	25.2 kB
DialogActions	--	60.7 kB	--	19 kB
DialogContent	--	60.8 kB	--	19.1 kB
DialogContentText	--	62.7 kB	--	19.7 kB
DialogTitle	--	62.9 kB	--	19.8 kB
Divider	--	61.2 kB	--	19.2 kB
docs.landing	--	55.5 kB	--	14.4 kB
Drawer	--	82.9 kB	--	25.7 kB
ExpansionPanelActions	--	60.7 kB	--	19 kB
ExpansionPanelDetails	--	60.6 kB	--	18.9 kB
ExpansionPanelSummary	--	76.7 kB	--	24.1 kB
Fab	--	75.4 kB	--	23.4 kB
Fade	--	22.2 kB	--	7.66 kB
FilledInput	--	72.2 kB	--	22.3 kB
FormControl	--	63 kB	--	19.5 kB
FormControlLabel	--	64.1 kB	--	20.1 kB
FormGroup	--	60.6 kB	--	19 kB
FormHelperText	--	61.9 kB	--	19.4 kB
FormLabel	--	62.1 kB	--	19.2 kB
Grid	--	63.7 kB	--	20 kB
GridList	--	61.1 kB	--	19.2 kB
GridListTile	--	62.3 kB	--	19.5 kB
GridListTileBar	--	61.8 kB	--	19.4 kB
Grow	--	22.8 kB	--	7.79 kB
Hidden	--	64.5 kB	--	20.2 kB
Icon	--	61.4 kB	--	19.2 kB
IconButton	--	74.7 kB	--	23.2 kB
Input	--	71.1 kB	--	22.1 kB
InputAdornment	--	63.7 kB	--	20.1 kB
InputBase	--	69.2 kB	--	21.7 kB
InputLabel	--	63.9 kB	--	19.9 kB
LinearProgress	--	64 kB	--	19.9 kB
Link	--	65.2 kB	--	20.7 kB
List	--	61 kB	--	18.9 kB
ListItem	--	75.7 kB	--	23.6 kB
ListItemAvatar	--	60.7 kB	--	19 kB
ListItemIcon	--	60.8 kB	--	19 kB
ListItemSecondaryAction	--	60.6 kB	--	19 kB
ListItemText	--	63.6 kB	--	20 kB
ListSubheader	--	61.4 kB	--	19.3 kB
Menu	--	86.9 kB	--	27.3 kB
MenuItem	--	76.7 kB	--	23.9 kB
MenuList	--	64.6 kB	--	20.1 kB
MobileStepper	--	66.3 kB	--	20.7 kB
Modal	--	14.2 kB	--	4.98 kB
NativeSelect	--	75.4 kB	--	23.7 kB
NoSsr	--	2.19 kB	--	1.03 kB
OutlinedInput	--	72.6 kB	--	22.5 kB
Paper	--	60.9 kB	--	18.9 kB
Popover	--	81.2 kB	--	25.1 kB
Popper	--	28.6 kB	--	10.2 kB
Portal	--	2.87 kB	--	1.29 kB
Radio	--	81.2 kB	--	25.5 kB
RadioGroup	--	61.8 kB	--	19.3 kB
Rating	--	68.6 kB	--	22 kB
RootRef	--	4.43 kB	--	1.67 kB
Select	--	113 kB	--	33.5 kB
Skeleton	--	61.2 kB	--	19.3 kB
Slide	--	24.3 kB	--	8.27 kB
Slider	--	74.2 kB	--	23.4 kB
Snackbar	--	75.7 kB	--	23.6 kB
SnackbarContent	--	64.3 kB	--	20.2 kB
SpeedDial	--	84.6 kB	--	26.6 kB
SpeedDialAction	--	115 kB	--	36.4 kB
SpeedDialIcon	--	63.2 kB	--	19.8 kB
Step	--	61.2 kB	--	19.2 kB
StepButton	--	80.9 kB	--	25.4 kB
StepConnector	--	61.3 kB	--	19.3 kB
StepIcon	--	63.3 kB	--	19.7 kB
StepLabel	--	67.2 kB	--	21.1 kB
Stepper	--	63.4 kB	--	19.9 kB
styles/createMuiTheme	--	15.4 kB	--	5.43 kB
SvgIcon	--	61.7 kB	--	19.2 kB
SwipeableDrawer	--	90.3 kB	--	28.1 kB
Switch	--	79.7 kB	--	24.8 kB
Tab	--	74.9 kB	--	23.7 kB
Table	--	61.2 kB	--	19.2 kB
TableBody	--	60.7 kB	--	19 kB
TableCell	--	62.7 kB	--	19.7 kB
TableFooter	--	60.7 kB	--	19 kB
TableHead	--	60.7 kB	--	19 kB
TablePagination	--	139 kB	--	40.7 kB
TableRow	--	61.1 kB	--	19.1 kB
TableSortLabel	--	75.9 kB	--	24 kB
Tabs	--	84 kB	--	26.8 kB
TextareaAutosize	--	5.06 kB	--	2.11 kB
TextField	--	122 kB	--	35.5 kB
ToggleButton	--	74.7 kB	--	23.6 kB
ToggleButtonGroup	--	61.8 kB	--	19.4 kB
Toolbar	--	60.9 kB	--	19.1 kB
Tooltip	--	99.1 kB	--	31.3 kB
TreeView	--	65 kB	--	20.3 kB
Typography	--	62.3 kB	--	19.4 kB
useAutocomplete	--	12.2 kB	--	4.5 kB
useMediaQuery	--	2.49 kB	--	1.05 kB
Zoom	--	22.3 kB	--	7.67 kB

Generated by 🚫 dangerJS against fa6a6af

[oliviertassinari]

It seems that the trick only work on Chrome. It's brittle, I don't think that we should move forward with it. Instead, it seems more flexible to assume the pixel unit if none is provided. In the future, we might want to explore https://developers.google.com/web/updates/2018/03/cssom (as browser support increase)