Tooltip info should evaluate and display constant expressions of types

[Lokathor]

Given the following:

pub type Tile4 = [u32; (4 * 8 * 8) / 32];
pub type Charblock4 = [Tile4; 512];

• If one hovers the mouse over Charblock4 you will see pub type Charblock8 = [Tile8; 256], the full type.
• If one hovers the mouse over pub type Tile4 = [u32; _], which is missing the number of elements.

It would be greatly improved if the display could evaluate the expression and show that.
I completely understand if a full const evaluation engine can't be rigged into RA, but at least some const expressions (such as integer literal math) should be possible.

[Veykril]

#10933 should bring us a bit closer to being able to do this

cc #8655