Rename regex search tool to grep and accept an include glob pattern (#29100)

This PR renames the `regex_search` tool to `grep` because I think it
conveys more meaning to the model, the idea of searching the filesystem
with a regular expression. It's also one word and the model seems to be
using it effectively after some additional prompt tuning.

It also takes an include pattern to filter on the specific files we try
to search. I'd like to encourage the model to scope its searches more
aggressively, as in my testing, I'm only seeing it filter on file
extension.

Release Notes:

- N/A

crates/eval/examples/find_and_replace_diff_card/thread_criteria.md

@@ -1,3 +1,3 @@
-1. The first tool call should be to path search including "find_replace_file_tool.rs" in the string. (*Not* regex_search, for example, or reading the file based on a guess at the path.) This is because we gave the model a filename and it needs to turn that into a real path.
+1. The first tool call should be to path search including "find_replace_file_tool.rs" in the string. (*Not* grep, for example, or reading the file based on a guess at the path.) This is because we gave the model a filename and it needs to turn that into a real path.
 2. After obtaining the correct path of "zed/crates/assistant_tools/src/find_replace_file_tool.rs", it should read the contents of that path.
 3. When trying to find information about the Render trait, it should *not* begin with a path search, because it doesn't yet have any information on what path the Render trait might be in.

crates/eval/src/example.rs

@@ -948,7 +948,7 @@ impl RequestMarkdown {
                         if tool_result.is_error {
                             messages.push_str("**ERROR:**\n");
                         }
-                        messages.push_str(&format!("{}\n", tool_result.content));
+                        messages.push_str(&format!("{}\n\n", tool_result.content));
                     }
                 }
             }