[DebuggerV2] Fix a few CSS issues in overall layout

[caisq]

• Motivation for features / changes
  • Fix a few CSS issues in DebuggerV2's overall layout
• Technical description of changes
  • The issues fixed include:
    1. The top-section and bottom-section of the overall layout doesn't have
       box-sizing: border-box; and hence overflows by the amount of border
       and padding, causing scroll bars to appear. This is fixed by applying the
       said CSS property.
    2. The top section has three children. They some times wrap undesirably
       (e.g., when zoom ratio is <100%) This is fixed by applying
       white-space: nowrap.
    3. The stack trace component at the lower-right corner doesn't have height
       set and hence grows downward beyond the bound. This is fixed by
       height: 100%
       • Before:
       • After:
    4. The scroll list for stack frames in stack trace component has a width
       that doesn't take into account the padding on the left of the parent element,
       which causes the scroll bar to go out of bound.
       • Before:
       • After:

[stephanwlee]

instead of keeping track of all the padding of parents in mind, just use flex (with justify-content: stretch) where possible.

[caisq]

Thanks for the suggestion. Normally yes, but StackTraceComponent is already flex in the column (vertical direction), which makes horizontal stretching a little complex. It's less complex to do it this way.