Task LAV-1754: DESC USER + SHOW PARAMETERS IN USER read surfaces (apache#2216)

Add `DESC[RIBE] USER <name>` rendering real Snowflake's 44-row
property/value/default/description table via a new
`__snowflake$describe_user` UDF that joins the user's jsonb property bag
with a static property catalog (stored value wins over default; derived
rows NAME/TYPE/PASSWORD/has_*-flags/LOCK_DETAILS computed from the bag).
NULL cells render as the literal string 'null', matching real Snowflake.

Parser: add `User` variant to `DescribeObjectType` and parse `DESC USER`.
Rewriter: route `DESC USER` to the new UDF. Wire the missing-user 002003
error position (DESC USER / DESCRIBE USER prefixes) so the verbatim
error snapshot (code/message/data incl. line/pos) matches real Snowflake.

New compat tests (snapshots captured on real Snowflake): fresh user,
CREATE with properties, ALTER SET/UNSET, missing-user error (snapshot,
no pytest.raises), and SHOW PARAMETERS IN USER NETWORK_POLICY no-regression.

Co-authored-by: Claude <noreply@anthropic.com>

Author: sabir-akhadov-localstack

src/ast/mod.rs

@@ -11545,6 +11545,9 @@ pub enum DescribeObjectType {
     Sequence,
     /// `PIPE`
     Pipe,
+    /// `USER` (Snowflake)
+    /// <https://docs.snowflake.com/en/sql-reference/sql/desc-user>
+    User,
 }
 
 impl fmt::Display for DescribeObjectType {
@@ -11562,6 +11565,7 @@ impl fmt::Display for DescribeObjectType {
             DescribeObjectType::Stream => "STREAM",
             DescribeObjectType::Sequence => "SEQUENCE",
             DescribeObjectType::Pipe => "PIPE",
+            DescribeObjectType::User => "USER",
         })
     }
 }

src/parser/mod.rs

@@ -15399,6 +15399,7 @@ impl<'a> Parser<'a> {
                         Keyword::STREAM,
                         Keyword::SEQUENCE,
                         Keyword::PIPE,
+                        Keyword::USER,
                     ]) {
                         let object_type = match kw {
                             Keyword::TABLE => DescribeObjectType::Table,
@@ -15410,6 +15411,7 @@ impl<'a> Parser<'a> {
                             Keyword::STREAM => DescribeObjectType::Stream,
                             Keyword::SEQUENCE => DescribeObjectType::Sequence,
                             Keyword::PIPE => DescribeObjectType::Pipe,
+                            Keyword::USER => DescribeObjectType::User,
                             _ => return self.expected("a describe object type", self.peek_token()),
                         };
                         let object_name = self.parse_object_name(false)?;