Cleanup: Sort node type definitions alphabetically

Previously we had a lot merge conflicts since we always put the most
recently added node at the bottom. By sorting the list we will have
one fewer merge conflict when a node is added in most cases.

Cleanup: Reorder class variable declarations

The order was arbitrary, and rearranging the declarations
makes the class look less messy, and makes room for future comments.

Cleanup: Whitespace, add doxygen sections

The sections aren't helpful at the moment, but I will add more code
here soon that will benefit more from the visual separation.

Cleanup: Use a helper function for repetitive code

Retrieving data from the component can be done in a separate function
to save some repetition.

Functions: Add materialize methods for generic mutable virtual array

Similar to how `GVArray_For_VArray` implements `materialize_impl` to
forward the work to its non-generic virtual array, we can do the same
thing for the mutable version, `GVMutableArray_For_VMutableArray`.

This commit should have no visible changes, since as far as I can tell
the only user of this class does not implement special materialize
methods anyway.

Fix: Curve resample duplicates last point for cyclic splines

The last point of the output was at the same location as the
first point of a cyclic spline. The fix is simple, just account for
the cyclic when choosing the sample edge length, and don't
hard code the last sample.

Fix T88126: Curve resample crash for single point input

The spline `length` function assumed that the curve always had evaluated
edges. That is clearly false. This commit adds a check to `length` and a
special case for a single point in the curve resample node.

Geometry Nodes: Improve point instance node performance

This commit uses two changes to improve the performance of the point
instance node.

**Prevent Reallocations**
At 64 bytes, the transform matrix for every instance is rather large,
so reallocating the vector as it grows can become a performance bottle-
neck. This commit reserves memory for the instances that will be added
to prevent unecessary reallocations as the instance vector grows.

In a test with 4 million instances of 3 objects in a collection, the
node was about 40% faster, from 370ms to 270ms for the node.

**Parallelization**
Currently the instances are added by appending to a vector. By changing
this slightly to fill indices instead, we can parallelize the operation
so that multiple threads can fill data at the same time. Tested on a
Ryzen 3700x, this reduced the runtime from the above 270ms to 44ms
average, bringing the total speedup to ~8x.

Note that displaying the instances in the viewport is still much slower
than the calculations in node, this change doesn't affect that.

Geometry Nodes: Refactor point instance node

This patch refactors the instance component to make use of the earlier
refactoring in rB4599cea15dcf. Now we don't have to build an array of
instance references the size of the point domain, and we can gather the
possible instances only once and use the same vector for all component
types. Generally the node should be a bit faster and use less memory.

The logic is moved around a bit, especially the hashing of the ID
attribute to pick from the instance list, but the result is unchanged.

Differential Revision: https://developer.blender.org/D11203

Fix: Curve to mesh node assert when last profile segment is vector

We need to always add a single point to the last cyclic segment that
completes the loop, because that includes the starting point of the
evaluated edge. The existing code forgot about that point.