Update casing of "OpenAI" in identifiers to match Rust conventions (#6940)

This PR updates the casing of "OpenAI" when used in Rust identifiers to
match the [Rust naming
guidelines](https://rust-lang.github.io/api-guidelines/naming.html):

> In `UpperCamelCase`, acronyms and contractions of compound words count
as one word: use `Uuid` rather than `UUID`, `Usize` rather than `USize`
or `Stdin` rather than `StdIn`.

Release Notes:

- N/A

crates/semantic_index/src/semantic_index.rs

@@ -8,7 +8,7 @@ mod semantic_index_tests;
 
 use crate::semantic_index_settings::SemanticIndexSettings;
 use ai::embedding::{Embedding, EmbeddingProvider};
-use ai::providers::open_ai::OpenAIEmbeddingProvider;
+use ai::providers::open_ai::OpenAiEmbeddingProvider;
 use anyhow::{anyhow, Context as _, Result};
 use collections::{BTreeMap, HashMap, HashSet};
 use db::VectorDatabase;
@@ -91,7 +91,7 @@ pub fn init(
 
     cx.spawn(move |cx| async move {
         let embedding_provider =
-            OpenAIEmbeddingProvider::new(http_client, cx.background_executor().clone()).await;
+            OpenAiEmbeddingProvider::new(http_client, cx.background_executor().clone()).await;
         let semantic_index = SemanticIndex::new(
             fs,
             db_file_path,