Summarize large constants that may appear in Jaxpr literals
Once we enable `config.use_simplified_jaxpr_constants` we can end
up with potentially large constants in Jaxprs. Instead of printing
non-scalars, we summarize them as `[...]`.
For example, if before a Jaxpr with constants would be printed
as:
```
{ lambda a:f32[256]; b:f32[]. let in (b, 1.0:f32[], a) }
```
now would be printed as
```
{ lambda a:f32[]. let in (a, 1.0:f32[], [...]:f32[256) }
```
In particular, this summarization does not increse the number of
lines in Jaxpr printing.
