[5.x] Fix implied route views

[duncanmcclean]

This pull request fixes an error when using implied route views, like this:

Route::statamic('my-page'); // Implies 'my-page'

The error was happening because the provided $view was a Stringable object, rather than an actual string. I've replaced Str::of(...)->ltrim(...) with a simple ltrim.

Fixes #11568.