[Feature] Watch included files (e.g. \input) to reflect changes

[DominikPeters]

This would require identifying all child files, sending their contents to TeXpresso (using the open command), and keeping a rope data structure for their contents. For identifying child files, code from the LaTeX Workshop extension could be adapted, see for example

https://github.com/James-Yu/LaTeX-Workshop/blob/fe6a08e9aa26ba4e2594d81a4b5baf636457d89e/src/utils/inputfilepath.ts#L18-L20

https://github.com/James-Yu/LaTeX-Workshop/blob/fe6a08e9aa26ba4e2594d81a4b5baf636457d89e/src/core/cache.ts#L278-L284

[let-def]

Alternatively, I can extend TeXpresso to notify the editor when a file is included.