Apply TextUtils, ensuring consistent line numbering

* in search_text
* in MatchedConsecutiveLines.from_file_contents

CHANGELOG.md

@@ -33,7 +33,9 @@ Status of the `main` branch. Changes prior to the next official version change w
   - During project creation, language composition percentages are now computed relative to the total number 
     of recognised source files instead of all files, i.e. unrecognised files are ignored in the percentage 
     computation.
-  - Fix: Use LSP-compliant line splitting ("\n", "\r\n" and "\r" can define line breaks)
+  - Fix: Use LSP-compliant line splitting ("\n", "\r\n" and "\r" can define line breaks); previously only "\n" considered
+  - Fix: Apply consistent line splitting across tools, uniformly applying the LSP splitting semantics; 
+    affects `search_text` used by `search_for_pattern` tool (reported in #1684)
 
 * CLI:
   - Fix `--project-from-cwd` hijacking git worktrees nested under a Serena project. `find_project_root`

src/serena/util/text_utils.py

@@ -100,7 +100,7 @@ class MatchedConsecutiveLines:
     def from_file_contents(
         cls, file_contents: str, line: int, context_lines_before: int = 0, context_lines_after: int = 0, source_file_path: str | None = None
     ) -> Self:
-        line_contents = file_contents.split("\n")
+        line_contents = TextUtils.split_lines(file_contents)
         start_lineno = max(0, line - context_lines_before)
         end_lineno = min(len(line_contents) - 1, line + context_lines_after)
         text_lines: list[TextLine] = []
@@ -169,7 +169,7 @@ def search_text(
         raise ValueError("Pass either content or source_file_path")
 
     matches = []
-    lines = content.splitlines()
+    lines = TextUtils.split_lines(content)
     total_lines = len(lines)
 
     # Convert pattern to a compiled regex if it's a string
@@ -185,8 +185,8 @@ def search_text(
         end_pos = match.end()
 
         # Find the line numbers for the start and end positions
-        start_line_num = content[:start_pos].count("\n")
-        end_line_num = content[:end_pos].count("\n")
+        start_line_num = TextUtils.get_line_from_index(content, start_pos)
+        end_line_num = TextUtils.get_line_from_index(content, end_pos)
 
         # Calculate the range of lines to include in the context
         context_start = max(0, start_line_num - context_lines_before)