### What changes were proposed in this pull request?
Make the field name matching between Avro and Catalyst schemas, on both the reader and writer paths, respect the global SQL settings for case sensitivity (i.e. case-insensitive by default). `AvroSerializer` and `AvroDeserializer` share a common utility in `AvroUtils` to search for an Avro field to match a given Catalyst field.
### Why are the changes needed?
Spark SQL is normally case-insensitive (by default), but currently when `AvroSerializer` and `AvroDeserializer` perform matching between Catalyst schemas and Avro schemas, the matching is done in a case-sensitive manner. So for example the following will fail:
```scala
val avroSchema =
"""
|{
| "type" : "record",
| "name" : "test_schema",
| "fields" : [
| {"name": "foo", "type": "int"},
| {"name": "BAR", "type": "int"}
| ]
|}
""".stripMargin
val df = Seq((1, 3), (2, 4)).toDF("FOO", "bar")
df.write.option("avroSchema", avroSchema).format("avro").save(savePath)
```
The same is true on the read path, if we assume `testAvro` has been written using the schema above, the below will fail to match the fields:
```scala
df.read.schema(new StructType().add("FOO", IntegerType).add("bar", IntegerType))
.format("avro").load(testAvro)
```
### Does this PR introduce _any_ user-facing change?
When reading Avro data, or writing Avro data using the `avroSchema` option, field matching will be performed with case sensitivity respecting the global SQL settings.
### How was this patch tested?
New tests added to `AvroSuite` to validate the case sensitivity logic in an end-to-end manner through the SQL engine.
Closes#31201 from xkrogen/xkrogen-SPARK-34133-avro-serde-casesensitivity-errormessages.
Authored-by: Erik Krogen <xkrogen@apache.org>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>
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