[Button] Improve horizontal padding

[mbrookes]

Closes #17634

In addition to apply the change discussed in #17634, it fixes some inconsistencies for small and large sizes with text and outlined variants, and adds text for these changes.

Arguably a breaking change for:

• Layout (minor button size changes)
• Customization (class name changes)

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

[mui-pr-bot]

@material-ui/core: parsed: +0.11% , gzip: +0.09%

Details of bundle changes.

Comparing: 05c533b...403c281

bundle	parsed diff	gzip diff	prev parsed	current parsed	prev gzip	current gzip
@material-ui/core	+0.11% 🔺	+0.09% 🔺	332,538	332,913	90,732	90,815
@material-ui/core/Paper	0.00%	0.00%	68,935	68,935	20,541	20,541
@material-ui/core/Paper.esm	0.00%	0.00%	62,372	62,372	19,275	19,275
@material-ui/core/Popper	0.00%	0.00%	28,405	28,405	10,172	10,172
@material-ui/core/Textarea	0.00%	0.00%	5,082	5,082	2,136	2,136
@material-ui/core/TrapFocus	0.00%	0.00%	3,766	3,766	1,596	1,596
@material-ui/core/styles/createMuiTheme	0.00%	0.00%	16,348	16,348	5,818	5,818
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@material-ui/system	0.00%	0.00%	15,581	15,581	4,341	4,341
Button	+0.48% 🔺	+0.27% 🔺	78,772	79,147	24,043	24,109
Modal	0.00%	0.00%	14,542	14,542	5,113	5,113
Portal	0.00%	0.00%	2,907	2,907	1,318	1,318
Rating	0.00%	0.00%	70,238	70,238	21,929	21,929
Slider	0.00%	0.00%	75,379	75,379	23,260	23,260
colorManipulator	0.00%	0.00%	3,835	3,835	1,519	1,519
docs.landing	0.00%	0.00%	54,267	54,267	14,344	14,344
docs.main	+0.06% 🔺	+0.04% 🔺	588,062	588,437	188,043	188,120
packages/material-ui/build/umd/material-ui.production.min.js	+0.12% 🔺	+0.08% 🔺	303,356	303,722	87,276	87,350

Generated by 🚫 dangerJS against 403c281

[oliviertassinari]

@mbrookes The padding changes look great!

I see a way to work around the customization breaking change I couldn't see previously 🤦‍♂️. I'm adding another commit for it.

Regarding #17638, do you think that we should give him the credit or continue here?

[mbrookes]

do you think that we should give him the credit or continue here?

All the same once it's merged, so whichever you prefer.

[oliviertassinari]

Customization (class name changes)

This one should be addressed.

Layout (minor button size changes)

The master branch has 3 other changes (MenuItem min-height change, Table spec update and Chip spec update) that have a similar impact. I'm OK if we release it in the next version (v4.5.0). I can't think of any worth-case impact that would break people application. Still, we need to be cautious.

[mbrookes]

I can't think of any worst-case impact that would break peoples application

Neither can I. I think it should be safe enough.