[C++] Cast float to decimal truncates

Even with all of the cast options to allow truncation and overflow set to False, cast from double to decimal truncates.

Short reproducer in R:

```Java

library(arrow, warn.conflicts = FALSE)

a <- Scalar$create(sqrt(2))
a
#> Scalar
#> 1.4142135623730951

a$cast(decimal(5, 1))
#> Scalar
#> 1.4
```

Longer version that shows the cast options:

```Java

library(arrow, warn.conflicts = FALSE)
library(dplyr, warn.conflicts = FALSE)

tab <- arrow_table(a = sqrt(2))
tab
#> Table
#> 1 rows x 1 columns
#> $a

tab$a
#> ChunkedArray
#>
#> [
#> [
#> 1.4142135623730951
#> ]
#> ]

# See that all of the cast options are false:
tab %>%
mutate(b = cast(a, decimal(5, 1)))
#> Table (query)
#> a: double
#> b: decimal128(5, 1) (cast(a, {to_type=decimal128(5, 1), allow_int_overflow=false, allow_time_truncate=false, allow_time_overflow=false, allow_decimal_truncate=false, allow_float_truncate=false, allow_invalid_utf8=false}))
#>
#> See $.data for the source Arrow object

new_tab <- tab %>%
mutate(b = cast(a, decimal(5, 1))) %>%
compute()
new_tab
#> Table
#> 1 rows x 2 columns
#> $a
#> $b

new_tab$b
#> ChunkedArray
#>
#> [
#> [
#> 1.4
#> ]
#> ]
```

**Reporter**: [Neal Richardson](https://issues.apache.org/jira/browse/ARROW-17606) / @nealrichardson

_{**Note**: *This issue was originally created as [ARROW-17606](https://issues.apache.org/jira/browse/ARROW-17606). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

Run the supplied R reproducer and inspect the C++ cast entry point for double-to-decimal handling, including the listed cast options. Done means casting with allow_float_truncate=false and allow_decimal_truncate=false no longer silently produces 1.4, with coverage for the reported behavior.

Written by the indexing model from the issue text.