Improve memory efficiency of Modal C0 Bases

Leaving a record here of the issue raised by @pmartorell in [this PR](https://github.com/gridap/GridapEmbedded.jl/pull/68) of `GridapEmbedded`. Quoting @pmartorell:

> I have found an important bottleneck in memory consumption related with the usage of `CompressedArray` in both modal C0 basis and moment fitting measures. It seems that Gridap is not efficient with `CompressedArray` with a large amount of values, e.g., `CompressedArray(vals,1:length(vals))`. The usage of flat arrays instead will reduce the memory consumption up to one order of magnitude.

> A possible optimization would accommodate the Gridap constructors of `CellQuadrature` and `FESpaces` to flat arrays of quadrature and reference FEs, respectively. It is probably better to include this optimization in another PR.

Start with the referenced GridapEmbedded PR #68 and inspect Gridap's CellQuadrature and FESpaces constructors, focusing on their handling of CompressedArray values. Compare the existing representation with flat arrays for modal C0 bases and moment fitting measures; done means preserving behavior while substantially reducing memory consumption.

Written by the indexing model from the issue text.