Meshable as Subtype of MeshBuilder

[larsraph]

Objective

• Previously we manually implimented From<{Meshable}> for Mesh {} for every type to avoid colliding with blanket impl for From<impl MeshBuilder> for Mesh {}. This is ugly and hard to maintain.

Solution

• I made all types that we're Meshable impl MeshBuilder. Now Meshable also impl's Into through it's MeshBuilder trait while also getting a direct builder function.
• I changed the names of the functions because they would've been confusing with the new setup.