Editorial: clean up enumerated attribute preambles

[keithamus]

Helps with #9832

The input type and button type attribute tables had lengthly preambles that didn't conform to the editorial changes requested in #9832 so this PR changes them to use the "with the following keywords and states" copy. I haven't altered the tables; while they deviate from others - lacking a "Brief description" and adding two additional columns - they are good as-is.

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/form-elements.html ( diff )
/input.html ( diff )

[domenic]

I noticed one small inconsistency we might want to take care of: throughout the spec, two matches for

The missing value default and the invalid value default are

and four matches for

The missing value default and invalid value default are

[keithamus]

I've tackled one of these here as it relates to the input. Looks like the others can be tackled separately as they'll need tables anyway. Tackled in #9947.

Also looks like there's an inconsistency in ordering. I count 10 matches for missing value default and invalid while there are 6 for invalid value default and missing. See #9947 for a separate cleanup of these sections.