id(dtype) of builtin vectors not in real_type_ids

[neozhaoliang]

To reproduce:

import taichi as ti

vec3 = ti.math.vec3
print(id(vec3.dtype))
print(ti.types.primitive_types.real_type_ids)

The result gives

140376791869680
[140376797782384, 140376797803760, 140376797803888, 9489216]

The id of the f32 type of vec3 is not in ti.types.real_type_ids.

This mismatch has the effect that the built-invec2/vec3/vec4 cannot be used as type hints since this line of code checks the id of the needed type.

Shall we change that line referenced above in kernel_impl.py to the following?

if needed.dtype in primitive_types.real_types:

[strongoier]

Some notes for people interested in the cause of this issue -

The type of default_fp is actually DataType in C++, and a DataType stores a pointer to its actual Type. The actual Type is unique, but the DataType wrapper can be different.