docs: fix additional comment typos across renderer and selection

Correct scrambled FIXME wording in InputHandler, "however" in
DomRenderer, duplicate "the" in selection code, "separate" and grammar
in DomRendererRowFactory, and "may cause" in WebglRenderer.

Co-authored-by: Cursor <cursoragent@cursor.com>

addons/addon-webgl/src/WebglRenderer.ts

@@ -667,7 +667,7 @@ export class WebglRenderer extends Disposable implements IRenderer {
     // The the size of the canvas on the page. It's important that this rounds to nearest integer
     // and not ceils as browsers often have floating point precision issues where
     // `window.devicePixelRatio` ends up being something like `1.100000023841858` for example, when
-    // it's actually 1.1. Ceiling may causes blurriness as the backing canvas image is 1 pixel too
+    // it's actually 1.1. Ceiling may cause blurriness as the backing canvas image is 1 pixel too
     // large for the canvas element size.
     this.dimensions.css.canvas.height = Math.round(this.dimensions.device.canvas.height / this._devicePixelRatio);
     this.dimensions.css.canvas.width = Math.round(this.dimensions.device.canvas.width / this._devicePixelRatio);