Create basic theme service

Part of #4184

src/browser/renderer/shared/CellColorResolver.ts

@@ -1,6 +1,6 @@
 import { ISelectionRenderModel } from 'browser/renderer/shared/Types';
 import { ICoreBrowserService } from 'browser/services/Services';
-import { IColorSet } from 'browser/Types';
+import { IColorSet, ReadonlyColorSet } from 'browser/Types';
 import { Attributes, BgFlags, FgFlags } from 'common/buffer/Constants';
 import { IDecorationService } from 'common/services/Services';
 import { ICellData } from 'common/Types';
@@ -26,7 +26,7 @@ export class CellColorResolver {
 
   constructor(
     private readonly _terminal: Terminal,
-    private _colors: IColorSet,
+    private _colors: ReadonlyColorSet,
     private readonly _selectionRenderModel: ISelectionRenderModel,
     private readonly _decorationService: IDecorationService,
     private readonly _coreBrowserService: ICoreBrowserService

src/browser/renderer/shared/CharAtlasCache.ts

@@ -5,7 +5,7 @@
 
 import { TextureAtlas } from 'browser/renderer/shared/TextureAtlas';
 import { Terminal } from 'xterm';
-import { IColorSet, ITerminal } from 'browser/Types';
+import { ITerminal, ReadonlyColorSet } from 'browser/Types';
 import { ICharAtlasConfig, ITextureAtlas } from 'browser/renderer/shared/Types';
 import { generateConfig, configEquals } from 'browser/renderer/shared/CharAtlasUtils';
 
@@ -27,7 +27,7 @@ const charAtlasCache: ITextureAtlasCacheEntry[] = [];
  */
 export function acquireTextureAtlas(
   terminal: Terminal,
-  colors: IColorSet,
+  colors: ReadonlyColorSet,
   scaledCellWidth: number,
   scaledCellHeight: number,
   scaledCharWidth: number,

src/browser/renderer/shared/CharAtlasUtils.ts

@@ -6,10 +6,10 @@
 import { ICharAtlasConfig } from './Types';
 import { Attributes } from 'common/buffer/Constants';
 import { Terminal } from 'xterm';
-import { IColorSet } from 'browser/Types';
+import { IColorSet, ReadonlyColorSet } from 'browser/Types';
 import { NULL_COLOR } from 'common/Color';
 
-export function generateConfig(scaledCellWidth: number, scaledCellHeight: number, scaledCharWidth: number, scaledCharHeight: number, terminal: Terminal, colors: IColorSet, devicePixelRatio: number): ICharAtlasConfig {
+export function generateConfig(scaledCellWidth: number, scaledCellHeight: number, scaledCharWidth: number, scaledCharHeight: number, terminal: Terminal, colors: ReadonlyColorSet, devicePixelRatio: number): ICharAtlasConfig {
   // null out some fields that don't matter
   const clonedColors: IColorSet = {
     foreground: colors.foreground,