Fix crash when dragging nodes

The `bNodeLinkDrag` struct was NULL when dragging a node instead of
a link. It is allocated with `calloc` anyway, so this field doesn't
need to be explitely cleared.

Cleanup: Use span and float matrix type in direct boolean code

This commit includes a few simple improvements to the direct mesh
boolean code added recently.
- Passing the transforms and meshes to `direct_mesh_boolean` as spans
makes the function easier to call from C++.
- The definition of `TransMat`, was unecessary when we have the
`float4x4` type already used elsewhere in C++ code.

Differential Revision: https://developer.blender.org/D10592

Geometry Nodes: Attribute search drop-down

This commit adds a search for existing attributes when you click
on an attribute field. This is useful because otherwise you have
to remember which attributes should be available at each node in
the tree.

The fundamental complication is that this information is not
accessible statically. So the search data is only a cache from
the previous node tree evaluation. The information is added
with `BKE_nodetree_attribute_hint_add`, currently for every
input geometry socket for a single node.

This is only an initial implementation, and later versions will
expose the data type and domain of the attributes.

Differential Revision: https://developer.blender.org/D10519

UI: Expose an "is first search" boolean to search button callbacks

Currently when you open an RNA collection search button, like a
vertex group selector, the search filter isn't applied until you
start typing, in order to display every option at the start.
Otherwise they wouldn't be visible, since the search filter would
run for the current text.

Currently this check happens in one place, but it relies on the
`changed` value of `uiBut`. This is fine in the interface directory,
but anywhere else it would require exposing `uiBut.changed`, which
is probably too low-level to expose.

The solution is adding an `is_first` argument to the search callbacks,
which is nice for a few reasons:
- They work at a higher level of abstraction, meaning they don't
have to worry about how exactly to tell if this is the first
search.
- It makes it easier to do special behavior when the search menu
is first opened.
- Then, obviously, it makes that state accessible without including
`interface_intern.h`.

Needed for attribute search: T85658

Differential Revision: https://developer.blender.org/D10528

Fix Node UI Storage Threading Issues

Since the same node tree can be used in modifiers on different objects,
there can be multiple threads writing to the maps in the node tree UI
storage at the same time. The additions for attribute name hints and
error messages made it so this would often cause a crash or at least
an ASAN report. This patch adds locks to prevent multiple threads
from using the maps concurrently.

In a brief test I actually didn't observe a crash without the global
`bNodeTree` UI storage mutex, but I think it's necessary for the change
to be correct, and I did notice some unfreed memory without it anyway.
Ideally it would be in a node tree runtime struct though.

Differential Revision: https://developer.blender.org/D10577

Fix build error after last commit

Cleanup: Rename node UI storage function

"ensure" makes more sense in this case because the function actually
adds an item to the map if one doesn't exist yet.

UI: Correct output attribute name in proximity node

I made an incorrect comment in patch review that "Location"
should be used instead of position. "Position" is more appropriate
here since it refers to generic data rather than an object origin.
"Position" is also the name we chose for the attribute for this reason.

Fix T84953: Incorrect tooltip for dragging collections

"Shift to parent" does not make any sense for collections since they
don't have parenting like objects. This commit just adds a simple check
for whether the first drag ID is an object before displaying
that part of the message.

Differential Revision: https://developer.blender.org/D10203

UI: Fix icon width and padding in search menus

Previously the padding size and the width saved for the icon were
constant regardless of the zoom level. This resulted in overlapping
icons and text, and ugly padding with more extreme zoom levels.
We can retrieve the size of the row from the `rect` argument.