[core] Upgrade deepmerge

[TrySound]

Still no esm but at least we got rid from umd wrapper here.

Details are here
TehShrike/deepmerge#155

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

[mui-pr-bot]

Details of bundle changes.

Comparing: 7d826a9...8f2c5a9

bundle	parsed diff	gzip diff	prev parsed	current parsed	prev gzip	current gzip
@material-ui/core	+0.05% 🔺	+0.02% 🔺	327,349	327,497	90,365	90,382
@material-ui/core/Paper	+0.22% 🔺	+0.05% 🔺	68,290	68,438	20,375	20,386
@material-ui/core/Paper.esm	+0.24% 🔺	+0.12% 🔺	61,574	61,722	19,155	19,178
@material-ui/core/Popper	0.00%	0.00%	28,942	28,942	10,408	10,408
@material-ui/core/Textarea	0.00%	0.00%	5,505	5,505	2,365	2,365
@material-ui/core/TrapFocus	0.00%	0.00%	3,753	3,753	1,576	1,576
@material-ui/core/styles/createMuiTheme	+0.92% 🔺	+0.36% 🔺	16,012	16,160	5,793	5,814
@material-ui/core/useMediaQuery	0.00%	0.00%	2,595	2,595	1,103	1,103
@material-ui/lab	+0.11% 🔺	+0.04% 🔺	137,896	138,044	42,523	42,540
@material-ui/styles	+0.29% 🔺	+0.10% 🔺	51,699	51,847	15,348	15,364
@material-ui/system	+0.96% 🔺	+0.89% 🔺	15,428	15,576	4,395	4,434
Button	+0.18% 🔺	+0.08% 🔺	84,442	84,590	25,738	25,759
Modal	0.00%	0.00%	14,515	14,515	5,088	5,088
Portal	0.00%	0.00%	3,471	3,471	1,573	1,573
Slider	+0.20% 🔺	+0.04% 🔺	74,976	75,124	23,292	23,302
colorManipulator	0.00%	0.00%	3,904	3,904	1,543	1,543
docs.landing	0.00%	0.00%	54,338	54,338	13,762	13,762
docs.main	+0.02% 🔺	+0.01% 🔺	647,009	647,158	203,904	203,926
packages/material-ui/build/umd/material-ui.production.min.js	+0.07% 🔺	-0.00%	299,721	299,920	85,971	85,969

Generated by 🚫 dangerJS against 8f2c5a9

[TrySound]

Ah, looks like some code was added after 3.2
https://bundlephobia.com/[email protected]

[eps1lon]

Ah, looks like some code was added after 3.2
bundlephobia.com/[email protected]

Should be the enumerable symbols support. I guess we still want that just in case.

[eps1lon]

@TrySound Thanks!