Non-scalar Matrix Field bugs

## Describe the bug
In the process of working the RosSSP timestepper, @Sbozzolo has uncovered 4 bugs in the Field/FieldMatrix broadcasting machinery:
- ~Division (not multiplication) of a Field of BandMatrixRows of non-scalars by a scalar throws an error~ [fixed in #2014]
- Multiplciation/division of a FieldMatrix by a scalar throws an error
- `Base.one` of a FieldMatrix with non-scalar subblocks generates a FieldMatrix with scalar subblocks, which then throws an error when combined with a FieldMatrix similar to the original
- `LinearAlgebra.ldiv!` generates `NaN`s when using a FieldMatrix with a single `UniformScaling` block.

## Steps to Reproduce
Using `W` to denote the `ImplicitEquationJacobian` used in ClimaAtmos, the bugs can be reproduced as follows:
- ~For the first bug, running `W.matrix[@name(f.u₃), @name(f.u₃)] ./ 2` reproduces the error~
- For the second bug, running `W.matrix .* 2` reproduces the error
- For the third bug, running `one(W.matrix)` generates the incorrect result, and running `W.matrix .+ one(W.matrix)` reproduces the error
- For the fourth bug, `ldiv!(x, W.matrix, b)` with a `matrix` that contains a single `UniformScaling` block and a FieldVector `x` that is full of ones generates the incorrect result