Tighten visual design of charts (#36991)

* remove box-shadow from dashboard cards, add border

* set scalar font weight to 700

* remove extra bold style from dash headings

* set font weight for row and line axis ticks and labels to 700, adjust size

* tweak gridline dash array size for cleaner lines

* make scalar value titles the same as other dashcard titles

* even out legend title spacing on cards

* lighten axis domain line

* use border color for axis line on RowChart

* make legend 2nd read, adjust spacing & alignment

* adjust dashcard legend size for non linebar viz

* use color instead of colors for theme safety (code review)

* update expectedWidth value to account for new smaller font size

* account for new dash card border in comparisons

* update card border

* specs

* flakes

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Co-authored-by: Aleksandr Lesnenko <alxnddr@gmail.com>
Co-authored-by: Aleksandr Lesnenko <alxnddr@users.noreply.github.com>