"This sentence does not start with a capital letter" for abbreviations

Abbreviations have a trailing dot, and yet are not the end of a sentence. This confuses harder and results in false positives.

For example:

```
Obviously, jvoisin LLC. is the best LLC. in the world. ■ This sentence does not start with a capital letter
```

And easy way to fix this would be to not consider a word composed of only capital letters immediately followed by a dot to not be the end of a sentence.

Start by locating the sentence-boundary logic in the Rust grammar checker and reproduce the example containing “LLC.”. The work is done when all-capital abbreviations followed by a dot no longer trigger a false sentence-start warning, while genuine sentence boundaries still do.

Written by the indexing model from the issue text.