docs:misc fixes (#9671)

Improve internal consistency in LangChain documentation
- Change occurrences of eg and eg. to e.g.
- Fix headers containing unnecessary capital letters.
- Change instances of "few shot" to "few-shot".
- Add periods to end of sentences where missing.
- Minor spelling and grammar fixes.

docs/api_reference/conf.py

@@ -156,7 +156,7 @@ html_context = {
 html_static_path = ["_static"]
 
 # These paths are either relative to html_static_path
-# or fully qualified paths (eg. https://...)
+# or fully qualified paths (e.g. https://...)
 html_css_files = [
     "css/custom.css",
 ]