Don't erase bookmark style when applying other styles

Add an automatic test for this.

Closes eng/ide/gnatstudio#24

Author: AnthonyLeonardoGracio

src_editor/src/src_editor_module.adb

@@ -2879,6 +2879,7 @@ package body Src_Editor_Module is
       Line_Highlighting.Add_Category (Messages_Styles (Low));
       Line_Highlighting.Add_Category (Messages_Styles (Informational));
       Line_Highlighting.Add_Category (Debugger_Current_Line_Style);
+      Line_Highlighting.Add_Category (Bookmark_Default_Style);
 
       Regenerate_Recent_Files_Menu (Kernel);
    end Register_Module;

testsuite/tests/gs.24.bookmarks.highlighting/main.adb

@@ -0,0 +1,6 @@
+procedure Main is
+   A : Integer := 1;
+   B : Integer := 2;
+begin
+   A := A + B;
+end Main;

testsuite/tests/gs.24.bookmarks.highlighting/test.cmd

@@ -0,0 +1 @@
+$GPS  --traceon=GPS.INTERNAL.Source_Editor.Buffer_Debug  --load=python:test.py

testsuite/tests/gs.24.bookmarks.highlighting/test.py

@@ -0,0 +1,44 @@
+"""
+This test checks that we correctly highlight the lines when
+bookmarks are being set. It also checks that the bookmark
+highlighting does not disappear when highlighting a part of
+the line.
+"""
+
+import GPS
+from gs_utils.internal.utils import *
+import gs_utils.internal.dialogs as dialogs
+
+
+EXPECTED_HIGHLIGHTING = ["", "Editor bookmarks", "", "", "", "", ""]
+
+
+@run_test_driver
+def test_driver():
+    # Create a bookmark in main.adb and check that the line
+    # is correctly highlighted.
+    buf = GPS.EditorBuffer.get(GPS.File("main.adb"))
+    editor_view = buf.current_view()
+    editor_view.goto(buf.at(2, 4))
+    GPS.execute_action("bookmark create")
+
+    gps_assert(
+        buf.debug_dump_line_highlighting(),
+        EXPECTED_HIGHLIGHTING,
+        "Line highlighting for bookmarks does not work",
+    )
+
+    # Search for 'Integer': this should highlight the search result
+    # on the same line as the bookmark. Verify that the bookmark highlighting
+    # is still present though.
+    s = dialogs.Search()
+    yield s.open_and_yield()
+    yield wait_idle()
+    s.pattern.set_text("Integer")
+    yield s.yield_find_all()
+
+    gps_assert(
+        buf.debug_dump_line_highlighting(),
+        EXPECTED_HIGHLIGHTING,
+        "Line highlighting for bookmarks has been removed after searching",
+    )

testsuite/tests/gs.24.bookmarks.highlighting/test.yaml

@@ -0,0 +1 @@
+title: 'gs.123.bookmarks.highlighting'