### What changes were proposed in this pull request?
This PR proposes to migrate the following function related commands to use `UnresolvedFunc` to resolve function identifier:
- DROP FUNCTION
- DESCRIBE FUNCTION
- SHOW FUNCTIONS
`DropFunctionStatement`, `DescribeFunctionStatement` and `ShowFunctionsStatement` logical plans are replaced with `DropFunction`, `DescribeFunction` and `ShowFunctions` logical plans respectively, and each contains `UnresolvedFunc` as its child so that it can be resolved in `Analyzer`.
### Why are the changes needed?
Migrating to the new resolution framework, which resolves `UnresolvedFunc` in `Analyzer`.
### Does this PR introduce _any_ user-facing change?
The message of exception thrown when a catalog is resolved to v2 has been merged to:
`function is only supported in v1 catalog`
Previously, it printed out the command used. E.g.,:
`CREATE FUNCTION is only supported in v1 catalog`
### How was this patch tested?
Updated existing tests.
Closes#29198 from imback82/function_framework.
Authored-by: Terry Kim <yuminkim@gmail.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>
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