Migrate dataframe tests to `insta`

[blaginin]

In #15178, we're switching hard-coded constants in tests to insta.

This issue targets updating dataframe tests (datafusion/core/tests/dataframe).

Examples of tests that need to be switched to insta

• datafusion/datafusion/core/tests/dataframe/dataframe_functions.rs

  Lines 114 to 123 in 1eefd13

  	let expected = [
  	"+--------------------+",
  	"| bit_length(test.a) |",
  	"+--------------------+",
  	"| 48 |",
  	"| 48 |",
  	"| 48 |",
  	"| 72 |",
  	"+--------------------+",
  	];

• datafusion/datafusion/core/tests/dataframe/dataframe_functions.rs

  Lines 1148 to 1151 in 1eefd13

  	let expected = "Sort: count(*) ASC NULLS LAST [count(*):Int64]\
  	\n Projection: count(*) [count(*):Int64]\
  	\n Aggregate: groupBy=[[test.b]], aggr=[[count(Int64(1)) AS count(*)]] [b:UInt32, count(*):Int64]\
  	\n TableScan: test [a:UInt32, b:UInt32, c:UInt32]";

• datafusion/datafusion/core/tests/dataframe/describe.rs

  Lines 67 to 78 in 1eefd13

  	let expected = [
  	"+------------+------+------+",
  	"| describe | a | b |",
  	"+------------+------+------+",
  	"| count | 1 | 1 |",
  	"| null_count | 0 | 0 |",
  	"| mean | null | null |",
  	"| std | null | null |",
  	"| min | a | null |",
  	"| max | a | null |",
  	"| median | null | null |",
  	"+------------+------+------+"

Check the original issue for tips on how to do the switch and examples of completed PRs.

[jsai28]

take