Some (poorly-implemented) LSPs can return an empty JSON object in
LSP responses, which could cause tokens to be nil, which would eventually
cause an error and a bad UI experience. This fix makes sure that the
tokens variable is always set to a non-nil value.

Problem:    Command line completion popup menu positioned wrong when using a
            terminal window.
Solution:   Position the popup menu differently when editing the command line.
            (Yegappan Lakshmanan, closes vim/vim#10050, closes vim/vim#10035)

https://github.com/vim/vim/commit/1104a6d0c2004d39e9b6cb8f804d12b628a69869

The test in the patch looks a bit hard to understand.
Add a Lua test that is more straightforward.

Co-authored-by: Yegappan Lakshmanan <yegappan@yahoo.com>

A zero-width click label isn't assigned to any click definition, so its
function name should be freed when filling click definitions.

Problem:    Cannot lock a variable in legacy Vim script like in Vim9.
Solution:   Make ":lockvar 0" work.

https://github.com/vim/vim/commit/a187c43cfe8863d48b2159d695fedcb71f8525c1

Co-authored-by: Bram Moolenaar <Bram@vim.org>

Click definitions are always filled for tabline, statusline and winbar,
so they should also be always filled for statuscolumn, otherwise it will
leak memory.

Note: this doesn't actually change the existing code much, because of a
typo in the existing code.

Problem:    Memory is leaked in tabline click definitions since
            https://github.com/neovim/neovim/pull/21008.
Solution:   Add back a call to `stl_clear_click_defs()` that was lost in
            the refactor PR.

Problem:
Failing Windows CI:
    FAILED   test/functional\options\defaults_spec.lua @ 361: XDG defaults with too long XDG variables are correctly set
    test\helpers.lua:134: Pattern "Failed to start server: no such file or directory: /X/X/X" not found in log (last 10 lines): Xtest-defaults-log:
    FAILED   test/functional\options\defaults_spec.lua @ 435: XDG defaults with XDG variables that can be expanded are not expanded
    test\helpers.lua:134: Pattern "Failed to start server: no such file or directory: %$XDG_RUNTIME_DIR%/" not found in log (last 10 lines): Xtest-defaults-log:

Solution:
The assert_log() statements are not relevant on Windows, because there
XDG_RUNTIME_DIR is not used for creating servers, it uses \\.pipe\….