tree: correctly cast float8 -> float4

[otan]

Resolves #73743, but there are many more issues.

Release note (bug fix): Previously, inserting or casting into a FLOAT4
with a range out of value would still work and be treated as a FLOAT8.
This can also means more precision is stored than necessary. This has
been resolved.

[cockroach-teamcity]

This change is 

[otan]

hmm

------- Stdout: -------
=== RUN   TestEval/opt/cast
    eval_test.go:48: 
        /go/src/github.com/cockroachdb/cockroach/pkg/sql/sem/tree/testdata/eval/cast:1207: '3.14'::jsonb::float4
        expected:
        3.14
        
        found:
        3.140000104904175
        --- FAIL: TestEval/opt/cast (0.01s)

maybe not