Fix regression in handling of text editor key bindings

Restore correct filtering and ordering of fallback key bindings.

- Only TextEditor and Global bindings are applicable to to IWpfTextView instancees
- TextEditor bindings should be prioritized before Global bindings

The recent `FallbackKeyProcessor` cleanup to address localization of Visual Studio scope names introduced a regression in which global bindings are considered before text editor bindings.  As a result, `Shift+Left` no longer works in the immediate window or when VsVim is disabled, but instead issues a command which throws the COM exception:

```
"The Command to execute is not enabled"
```