Add trace log level, traceCall decorator and use in webgl

- New 'trace' log level in the API, you should expect very spammy logs when
  trace is on and filter them down. As opposed to 'debug' which should be more
  readable.
- traceCall decorator logs the args and return value of the decorated method.
  Wecan use this on key functions in various parts of the code to assist
  debugging issues that are hard to reproduce such as #4665.
- Decorated a few webgl render methods for #4665.
- There's an early exit in traceCall when not on the trace log level so the
  runtime impact when not in trace is negligable.

Part of #4665

addons/xterm-addon-webgl/src/WebglRenderer.ts

@@ -17,7 +17,7 @@ import { CellData } from 'common/buffer/CellData';
 import { Attributes, Content, NULL_CELL_CHAR, NULL_CELL_CODE } from 'common/buffer/Constants';
 import { EventEmitter, forwardEvent } from 'common/EventEmitter';
 import { Disposable, getDisposeArrayDisposable, toDisposable } from 'common/Lifecycle';
-import { ICoreService, IDecorationService, IOptionsService } from 'common/services/Services';
+import { ICoreService, IDecorationService, ILogService, IOptionsService } from 'common/services/Services';
 import { CharData, IBufferLine, ICellData } from 'common/Types';
 import { IDisposable, Terminal } from 'xterm';
 import { GlyphRenderer } from './GlyphRenderer';
@@ -27,6 +27,7 @@ import { LinkRenderLayer } from './renderLayer/LinkRenderLayer';
 import { IRenderLayer } from './renderLayer/Types';
 import { COMBINED_CHAR_BIT_MASK, RenderModel, RENDER_MODEL_BG_OFFSET, RENDER_MODEL_EXT_OFFSET, RENDER_MODEL_FG_OFFSET, RENDER_MODEL_INDICIES_PER_CELL } from './RenderModel';
 import { IWebGL2RenderingContext } from './Types';
+import { traceCall } from 'common/services/LogService';
 
 export class WebglRenderer extends Disposable implements IRenderer {
   private _renderLayers: IRenderLayer[];
@@ -323,6 +324,7 @@ export class WebglRenderer extends Disposable implements IRenderer {
     return false;
   }
 
+  @traceCall
   public renderRows(start: number, end: number): void {
     if (!this._isAttached) {
       if (this._coreBrowserService.window.document.body.contains(this._core.screenElement!) && this._charSizeService.width && this._charSizeService.height) {