[V3] colorRampTexture with NEAREST textureFilter

Motivation

The TextureFilter of colorRampTexture is now only fixed to 'LINEAR'.
But in some case, the user may wish to use 'NEAREST' for color palette, especially using 'step' expression for raster-color.
No color interpolation is needed arround threshold value.

The attached images area drawn by following paint properties.

    'raster-color': [
            'step',
            ['raster-value'],
            'transparent', 0.3,
            '#00DCEA', 2.0,
            '#0005B9', 8.0,
            '#FFF000', 16.0,
            '#F50100'
    ],
    'raster-color-mix': [255, 0, 0, 0],
    'raster-color-range': [0, 255],
    'raster-opacity': 0.8,

Design Alternatives

Design

adding new paint property like raster-color-resampling: "nearest" | "linear" ("linear" as default)
or use existing paint property raster-resampling for raster-color-ramp.

Mock-Up

Concepts

Implementation

change L130 of draw_raster.js

from

tex.bind(gl.LINEAR, gl.CLAMP_TO_EDGE);

to

if(layer.paint.get('raster-color-resampling') === 'nearest') {
    tex.bind(gl.NEAREST, gl.CLAMP_TO_EDGE);
} else {
    tex.bind(gl.LINEAR, gl.CLAMP_TO_EDGE);
}

Read src/render/draw_raster.js around L130 first, where colorRampTexture is currently bound with LINEAR filtering. Confirm whether the new paint property or existing raster-resampling property should control sampling; done means NEAREST works for raster-color step expressions while LINEAR remains the default.