feat: Deephaven UI table databar support

[mattrunyon]

Changes needed for dh.ui databars

• Support for extracting data in viewport columns not listed in table.columns. This allows us to hide the aggregation columns for databars from the user but still get their data. If a column is not in table.columns then it will be added to viewport data via its name instead of model index
• Improved gradient rendering to be much more efficient
• Fixed opacity being ignored if a gradient was used
• Fixed some of the databar spacing (was 1px off center)
• Modified colorValueStyle to have overrides so if we pass a string we don't get back string | undefined when we know we'll get a string
• Modified resolveCssVariablesInRecord to always resolve CSS colors regardless of if they contain a variable