fix: address escape literal issue #21516

[SamAya21]

Which issue does this PR close?
Closes #21516

Rationale for this change
Issue #21516 reports that Spark-mode SQL string literals such as '\thello' and '\nhello' are treated as literal backslash text instead of using Spark-compatible escape handling. This fix should address all string functions not just soundex and length. This should improve matching functionality between pyspark and datafusion-spark

What changes are included in this PR?

• I added a Spark-only SQL parser option: 'datafusion.sql_parser.spark_string_literal_unescape'
• threaded the option through 'ParserOptions'
• updated 'datafusion/sql/src/expr/value.rs' to unescape string literals only when the Spark-only option is enabled
• enabled the option from 'with_spark_features()' in 'datafusion/spark/src/session_state.rs'
• updated tests and sqllogictest expectations and test snapshots

Are these changes tested?
Yes. I tested the change with these commands:

cargo test -p datafusion
cargo test -p datafusion-sql
cargo test -p datafusion-spark
cargo test --profile=ci --test sqllogictests

Are there any user-facing changes?
Yes, there are user-facing changes. In Spark mode, SQL string literals now use Spark-compatible backslash escape handling. Generic DataFusion SQL behavior is unchanged.

[kumarUjjawal]

Few points before the actual code review:

1. Always make sure you run the linter locally with all the tests passing
2. Follow the PT template
3. Please read the ai assisted pr guidelines https://datafusion.apache.org/contributor-guide/index.html#ai-assisted-contributions

[SamAya21]

Sorry about that, I hadn't seen I should've ran sqllogictests. How exactly would I run the linter locally or what webpage would I find that as I see that I had forgot to add the header to a test file I had created.

[kumarUjjawal]

Sorry about that, I hadn't seen I should've ran sqllogictests. How exactly would I run the linter locally or what webpage would I find that as I see that I had forgot to add the header to a test file I had created.

1. run cargo fmt: cargo fmt --all
2. run clippy: cargo clippy --workspace --all-features --all-targets -- --deny=warnings
3. run sqllogictest: make -C testing/runner test-sqlite