[Mosch0512]

What this does

Two follow-ups to #845 (the Server List window):

• What was typed stays an undo step of its own. A text field's edit became an undo step only once no widget was active. Leaving the field with a click on a button or box made that widget active, and its change joined the typed text in one step: renaming Helheim to Asgard and then clicking Move up gave one step "Move Asgard", and one Undo took back both. A name followed by a click into the description became one step too. Leaving a field now ends its edit as a step, and the list buttons, the test server box and the channel types first make what was typed a step before they change the groups.
• The editor bar names the undo step only for its tooltip. The bar asked for the names of the next Undo and Redo on every frame; for the Server List window that compared the group lists and formatted a text each frame while a change was typed. They are asked for only while a button is hovered, as before feat: server list as JSON with a Server List editor window #845.

docs/server-list.md now says what one undo step is.

Testing

• New Server List window tests in server_list_data_tests draw the window without a renderer, type into the name field and then press Move down, the test server box or the description field, and check that the typed name is an undo step of its own. The server list tests link Winmain.cpp for the editor's globals now, as the item tool tests do; TestImGuiContext moved to tests/data/TestImGuiContext.h for both.
• server_list_data_tests: 41/41 pass; the item tool tests (test_item_database_files, [editor]): 46/46 pass (Windows, Release, editor build).
• clang-format 21.1.8 on the changed lines.
• Not tried in the game yet.

Commits

1. test(data): the ImGui test context in a header of its own
2. fix(editor): what was typed in the Server List window stays an undo step of its own
3. perf(editor): the editor bar names its undo step only for the tooltip