Geometry Nodes: Get and set nodes for ID attribute

These nodes allow accessing and changing the stable/random ID used
for motion blur with instances and stable randomness.

Since rB40c3b8836b7a, the stable ID is a built-in attribute, so to be
consistent and allow changing it in the node tree like other built-in
attributes, it has get and set nodes.

Cleanup: Restore alphabetical order

Fix: Show node editor dot grid when there is no node tree

Fix: Inverted normal for one curve to mesh cap

Geometry Nodes: Only create instance IDs when they exist

Instance IDs serve no purpose for rendering when they aren't stable from
one frame to the next, and if the index is used in the end anyway, there
is no point in storing a vector of IDs and copying it around.

This commit exposes the `id` attribute on the instances component,
makes it optional-- only generated by default with the distribute points
on faces node.

Since the string to curves node only added the index as each instance's
ID, I removed it. This means that it would be necessary to add the ID
data manually if the initial index actually helps (when deleting only
certain characters, for example).

Differential Revision: https://developer.blender.org/D12980

Geometry Nodes: Support instances in the remove attribute node

This node is still hidden, but allowing removing the `id` attribute is
useful for testing, and possibly optimization in the future.

Geometry Nodes: Handle multiple grids in the volume to mesh node

In future use cases, a volume can contain many grids that represent the
density information. In this case, it's better if the volume to mesh node
creates a mesh based on all of the grids in the volume.

This is also a benefit to share-ability, since one doesn't have to
specify the grid name in the node. Instead, in the future we can have
a way to split particular grids into separate volumes, if only one
grid should be considered.

The code changes are relatively simple:
- Move the old volume to mesh node to the legacy folder.
- Run the volume to mesh node on all instance geometry, like elsewhere.
- Make the blenkernel's volume to mesh API a bit more specific.

Differential Revision: https://developer.blender.org/D12997

UI: Improve node editor breadcrumbs display

This patch upgrades node editor breadcrumbs to have slightly more
visual weight, to including the base path of object/modifier/world,
etc, have more visually pleasing spacing, and contain icons.

In the code, a generic "context path" is added to interface code.
The idea is that this could be used to draw other breadcrumbs in areas
like the property editor or the spreadsheet, and features could be added
to all of those areas at the same time.

Ideally we would be able to control the color of the breadcrumbs with a
specific theme color, but since they are drawn with the regular layout
system, that is not easily possible.

Thanks to @fabian_schempp for the original patch.

Differential Revision: https://developer.blender.org/D10413

Fix: Assert on startup from incorrect float property min

UI: Change node editor grid into a dot grid

This patch makes the background grid of the node editor a grid of dots
instead of lines. This makes the background look a bit more subtle and
reduces visual complexity. The dots are meant to provide a reference
when panning and zooming. Based on the design of @pablovazquez, and
a patch originally authored by @fabian_schempp.

The "Grid Levels" controls how many levels of dots are drawn. As the
editor zooms in, the higher levels of dots fade in, making them closer
together visually. The zoom factor at which each grid starts and ends
fading in is controllable in the code, and could be tweaked further
in the future. The new default value is 7, out of a range from 0 to 9.

Differential Revision: https://developer.blender.org/D10345