The webgl extension fails hard when an invalid cursorStyle value is set #3477
Description
Setting cursorStyle to "line" causes this exception:
[7072:0921/115334.522:INFO:CONSOLE(249)] "TypeError: this._cursorRenderers[n] is not a function
at e._render (vscode-file://vscode-app/d:/GitHub/microsoft/vscode/node_modules/xterm-addon-webgl/lib/xterm-addon-webgl.js:1:46909)
at e.onGridChanged (vscode-file://vscode-app/d:/GitHub/microsoft/vscode/node_modules/xterm-addon-webgl/lib/xterm-addon-webgl.js:1:46287)
at e.renderRows (vscode-file://vscode-app/d:/GitHub/microsoft/vscode/node_modules/xterm-addon-webgl/lib/xterm-addon-webgl.js:1:22525)
at t._renderRows (vscode-file://vscode-app/d:/GitHub/microsoft/vscode/node_modules/xterm/lib/xterm.js:1:162731)
at e._renderCallback (vscode-file://vscode-app/d:/GitHub/microsoft/vscode/node_modules/xterm/lib/xterm.js:1:160756)
at e._innerRefresh (vscode-file://vscode-app/d:/GitHub/microsoft/vscode/node_modules/xterm/lib/xterm.js:1:36928)
at vscode-file://vscode-app/d:/GitHub/microsoft/vscode/node_modules/xterm/lib/xterm.js:1:36644", source: vscode-file://vscode-app/d:/GitHub/microsoft/vscode/out/bootstrap-window.js (249)
We should handle this more gracefully, maybe by sanitizing the option at the time it's set (and Terminal.ctor). Can also check the other renderers to make sure they handle it fine, I think dom is fine,