Better error message when creating a block without passing a figure argument

[asinghvi17]

Currently, the error looks like this:

julia> LScene()
ERROR: MethodError: no method matching _block(::Type{LScene})
The function `_block` exists, but no method is defined for this combination of argument types.

Closest candidates are:
  _block(::Type{<:Makie.Block}, ::Union{Figure, Scene}, ::Any, ::Dict, ::Any; kwdict_complete)
   @ Makie ~/.julia/dev/Makie/src/makielayout/blocks.jl:317
  _block(::Type{<:Makie.Block}, ::Union{Figure, Scene}, ::Any...; bbox, kwargs...)
   @ Makie ~/.julia/dev/Makie/src/makielayout/blocks.jl:261
  _block(::Type{<:Makie.Block}, ::Union{GridPosition, GridSubposition}, ::Any...; kwargs...)
   @ Makie ~/.julia/dev/Makie/src/makielayout/blocks.jl:249

Stacktrace:
 [1] LScene(; kwargs::@Kwargs{})
   @ Makie ~/.julia/dev/Makie/src/makielayout/blocks.jl:240
 [2] LScene()
   @ Makie ~/.julia/dev/Makie/src/makielayout/blocks.jl:239
 [3] top-level scope
   @ REPL[3]:1

(note the lack of a grid position as the first arg)

We should change this to something like:

ArgumentError: when creating a $blocktype, you have not provided a layout position or a figure in which the block should exist as the first argument.

Make sure you provide this first argument, as so:

$blocktype(fig[i, j], ...)
$blocktype(fig, ...)

or so.