## What changes were proposed in this pull request?
When running a custom build of Spark which shades `commons-codec`, the `Sha1` expression generates code which fails to compile:
```
org.apache.spark.sql.catalyst.expressions.codegen.CodeGenerator: failed to compile: org.codehaus.commons.compiler.CompileException: File 'generated.java', Line 47, Column 93: A method named "sha1Hex" is not declared in any enclosing class nor any supertype, nor through a static import
```
This is caused by an interaction between Spark's code generator and the shading: the current codegen template includes the string `org.apache.commons.codec.digest.DigestUtils.sha1Hex` as part of a larger string literal, preventing JarJarLinks from being able to replace the class name with the shaded class's name. As a result, the generated code still references the original unshaded class name name, triggering an error in case the original unshaded dependency isn't on the path.
This problem impacts the `Sha1`, `Md5`, and `Base64` expressions.
To fix this problem and allow for proper shading, this PR updates the codegen templates to replace the hardcoded class names with `${classof[<name>].getName}` calls.
## How was this patch tested?
Existing tests.
To ensure that I found all occurrences of this problem, I used IntelliJ's "Find in Path" to search for lines matching the regex `^(?!import|package).*(org|com|net|io)\.(?!apache\.spark)` and then filtered matches to inspect only non-test "Usage in string constants" cases. This isn't _perfect_ but I think it'll catch most cases.
Closes#24655 from JoshRosen/fix-shaded-apache-commons.
Authored-by: Josh Rosen <rosenville@gmail.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>
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