MDEV-8320 Allow index usage for DATE(col) <=> const and YEAR <=> constbb-11.0-MDEV-8320

Rewrite datetime comparison conditions into sargeable. For example,
    YEAR(col) <= val  ->  col <= YEAR_END(val)
    YEAR(col) <  val  ->  col <  YEAR_START(val)
    YEAR(col) >= val  ->  col >= YEAR_START(val)
    YEAR(col) >  val  ->  col >  YEAR_END(val)
    YEAR(col) =  val  ->  col BETWEEN YEAR_START(val) AND YEAR_END(val)
Do the same with DATE(col), for example:
    DATE(col) <= val  ->  col <= DAY_END(val)

After such a rewrite index lookup on column "col" can be employed

1 files changed, 20 insertions, 0 deletions

diff --git a/sql/sql_lex.h b/sql/sql_lex.h
index 95ed308103d..7d8895f1e6c 100644
--- a/sql/sql_lex.h
+++ b/sql/sql_lex.h
@@ -2320,6 +2320,20 @@ public:
   bool uses_stored_routines() const
   { return sroutines_list.elements != 0; }
 
+  void set_date_funcs_used_flag()
+  {
+    date_funcs_used_flag= true;
+  }
+
+  /*
+    Returns TRUE if date functions such as YEAR(), MONTH() or DATE()
+    are used in this LEX
+  */
+  bool are_date_funcs_used() const
+  {
+    return date_funcs_used_flag;
+  }
+
 private:
 
   /**
@@ -2360,6 +2374,12 @@ private:
     be accessed while executing a statement.
   */
   uint32 stmt_accessed_table_flag;
+
+  /*
+    Flag indicating that date functions such as YEAR(), MONTH() or DATE() are
+    used in this LEX
+  */
+  bool date_funcs_used_flag= false;
 };