Fix VsButtonStyleKey to match TE button style #599

VsButtonStyleKey is matching the standard VS button style, but the TE button style is slightly different. Since we're only using this button style in TE sections, we should fix it to match TE.

TE button, non-hover and hover state, dark theme

TE button, non-hover and hover state, white theme

Our button, hover state, dark theme

Background and border need fixing

Our button, non-hover and hover state, white theme

Border needs fixing