x11: ensure some context is bound before calling glClientWaitSync

See merge request !2138

entrycompletion: Drop action support

See merge request !2136

Add a basic clipboard test

See merge request !2137

Since commit 972134ab we now call
glClientWaitSync for the vendor nvidia driver, to know when a frame
is ready for the compositor to process.

glClientWaitSync can be called regardless of which context is currently
bound, but if no context is bound at all, it returns 0 without
doing anything.

This commit checks for that edge case, and ensures a context gets
made current in the event no context is already current, before calling
glClientWaitSync.

This is not reproducing the failure I'm after, unfortunately.

This api has not really been kept up with current
user experiences in popups, and we're better off
just dropping it and letting people do their own
popups if they need custom UI.

gdk: Make gdk_keyval_to_unicode platform-independent

See merge request !2132

Fix entry completion

See merge request !2135

Explicitly state that the conversion does not
take locale into account, and point out GDK_KEY_KP_Decimal
as a candidate for special-casing.

Use gtk_widget_prepend_controller to supersede entry keynav
while the popup is open. This fixes selecting completions
with the keyboard - the Enter keypress was ending up
triggering GtkText::activate instead of inserting the
selected completion into the entry.

Add a variant of gtk_widget_add_controller that
inserts the controller at the beginning, instead
of the end. This will be used in entry completion
to make sure the entry completion key event handling
supersedes the entry one while the popup is open.

Keep this private for now, until we determine if
it needs to be public api.

We were adding event controllers at the end, but
announcing a change at the beginning, in
gtk_widget_add_controller. Fix that by emitting
::items-changed for the position where we actually
inserted the controller.

This helps with debugging.

x11: be more verbose when glClientWaitSync behaves unexpectedtly

See merge request !2133

When given a 0 timeout, glClientWaitSync is only supposed to return one
of three possible values:

 - GL_ALREADY_SIGNALED - fence fired
 - GL_WAIT_FAILED - there was an error
 - GL_TIMEOUT_EXPIRED - fence hasn't fired yet

In addition, it can also return GL_CONDITION_SATISFIED if a non-zero
timeout is passed, and the fence fires while waiting on the timeout.

Since commit 972134ab we now call
glClientWaitSync (with a 0 timeout), but one user is reporting it's
returning some value that's not one of the above four.

This commit changes the g_assert to a g_error so we can see what
value is getting returned.

May help with #2858

gtk-demo: Add a warning to the colors demo

See merge request !2131

The result of gdk_keyval_to_unicode should not depend
on the platform.

demos: Fix builds against Visual Studio headers

See merge request !2130

Explain that the big sizes cause lockups.

According to [1], '_timezone' is already used for a global variable in the
time.h system header that is supplied by Microsoft, so using that for our
variable name when we are including time.h either directly or indirectly
will cause trouble.

This renames such variables to '_tz' to avoid that

[1]: https://docs.microsoft.com/en-us/cpp/c-runtime-library/daylight-dstbias-timezone-and-tzname

Port icon browser

See merge request !2127

filter: Make GtkEveryFilter buildable

See merge request !2125

Due to an oversight, when multi filters were split into
any and every, any ended up with the listmodel and buildable
implementations, and every didn't get any.

Move the implementations up.

Improve listview-colors demo

See merge request !2123

Make the count label not jump around, as the model
is refilled.

Tests the previous commit and ensures that selecting 16M colors actually
works quickly (it does).

For now, we just look at SORT_ORDER_NONE to bypass any sorting.

Do it via the new size setting on the color list.

Also add an option to set the maximum size of the color list that it'll
be filled to so rudimentary performance testing is possible.

Hint: Do not select 16777216.

This reinstates commit c16848c2.

For now, limit it to 1<<12 so the sorters don't explode.

This way, the colors are furthest apart at the start and fill up the
remaining spots towards the end.

This makes it slightly slow, so not sure it should stay like this.

This eases adding a bunch of follow-up features. After those features
have landed, this functionality will be readded.

This reverts commit a1034085.

Wip/otte/for master

See merge request !2122

This showed up as a test failure when we get NULL as
selected item and then try to unref it. Luckily
get_selected_item is transfer none, so we don't have
to worry about it.