Table rendering support - registering/using custom cell renderers

[mofojed]

GridModel will need to have a way of specifying a new type of renderer on a per cell basis. Currently we just support rendering text, so that should be the default cell renderer, and then allow for registering/specifying different renderers. We can have a TextCellRenderer as the default, and BarGaugeRenderer packaged in @deephaven/grid, but not a default.

• Add a rendererForCell(column: ModelIndex, row: ModelIndex): CellRendererType and type CellRendererType = string
• Refactor text cell rendering to a separate class TextCellRenderer and use that from GridRenderer when rendering a cell by default (or if renderer not specified)
• Allow registering a different types of renderers that GridRenderer.drawCellContents will automatically call if there's a renderer specified for that cell
• Create BarGaugeRenderer, and an extension to GridModel for the details required for BarGaugeRenderer

We should be able to test this out in the style guide using a mock (similar to MockGridModel).

[dsmmcken]

Registering my expectation that gradient rendering use OKLab color space for interpolation.