Symbolic name codegen - optimize indexed access with integer literal

From discussion on https://github.com/Azure/bicep/pull/4138.

Rather than generating `[format('symbol[{0}]', 0)]` when building a fixed-index reference to an item in a symbolic name resource loop, we could instead just generate `symbol[0]`.

Start in the symbolic-name resource loop code-generation path discussed in issue #4254 and compare the generated indexed reference for an integer literal with the current format-based form. Done means fixed-index references emit the direct symbol[0]-style access rather than format('symbol[{0}]', 0); no specific file or test is named in the issue.

Written by the indexing model from the issue text.