MDEV-10138 Support for decimals up to 38 digits

Decimals with float, double and decimal now works the following way:

- DECIMAL_NOT_SPECIFIED is used when declaring DECIMALS without a firm number
  of decimals.  It's only used in asserts and my_decimal_int_part.
- FLOATING_POINT_DECIMALS (31) is used to mark that a FLOAT or DOUBLE
  was defined without decimals. This is regarded as a floating point value.
- Max decimals allowed for FLOAT and DOUBLE is FLOATING_POINT_DECIMALS-1
- Clients assumes that float and double with decimals >= NOT_FIXED_DEC are
  floating point values (no decimals)
- In the .frm decimals=FLOATING_POINT_DECIMALS are used to define
  floating point for float and double (31, like before)

To ensure compatibility with old clients we do:

- When storing float and double, we change NOT_FIXED_DEC to
  FLOATING_POINT_DECIMALS.
- When creating fields from .frm we change for float and double
  FLOATING_POINT_DEC to NOT_FIXED_DEC
- When sending definition for a float/decimal field without decimals
  to the client as part of a result set we convert NOT_FIXED_DEC to
  FLOATING_POINT_DECIMALS.
- variance() and std() has changed to limit the decimals to
  FLOATING_POINT_DECIMALS -1 to not get the double converted floating point.
  (This was to preserve compatiblity)
- FLOAT and DOUBLE still have 30 as max number of decimals.

Bugs fixed:

variance() printed more decimals than we support for double values.

New behaviour:
- Strings now have 38 decimals instead of 30 when converted to decimal
- CREATE ... SELECT with a decimal with > 30 decimals will create a column
  with a smaller range than before as we are trying to preserve the number of
  decimals.


Other changes
- We are now using the obsolete bit FIELDFLAG_LEFT_FULLSCREEN to specify
  decimals > 31
- NOT_FIXED_DEC is now declared in one place
- For clients, NOT_FIXED_DEC is always 31 (to ensure compatibility).
  On the server NOT_FIXED_DEC is DECIMAL_NOT_SPECIFIED (39)
- AUTO_SEC_PART_DIGITS is taken from DECIMAL_NOT_SPECIFIED
- DOUBLE conversion functions are now using DECIMAL_NOT_SPECIFIED instead of
  NOT_FIXED_DEC

mysql-test/r/func_str.result

@@ -731,7 +731,7 @@ t1	CREATE TABLE `t1` (
   `conv(130,16,10)` varchar(64) DEFAULT NULL,
   `hex(130)` varchar(6) NOT NULL,
   `char(130)` varbinary(4) NOT NULL,
-  `format(130,10)` varchar(37) NOT NULL,
+  `format(130,10)` varchar(45) NOT NULL,
   `left(_latin2'a',1)` varchar(1) CHARACTER SET latin2 NOT NULL,
   `right(_latin2'a',1)` varchar(1) CHARACTER SET latin2 NOT NULL,
   `lcase(_latin2'a')` varchar(1) CHARACTER SET latin2 NOT NULL,
@@ -1237,13 +1237,13 @@ create table t1 (i int);
 insert into t1 values (1000000000),(1);
 select lpad(i, 7, ' ') as t from t1;
 Catalog	Database	Table	Table_alias	Column	Column_alias	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
-def					t	253	7	7	Y	0	31	8
+def					t	253	7	7	Y	0	39	8
 t
 1000000
       1
 select rpad(i, 7, ' ') as t from t1;
 Catalog	Database	Table	Table_alias	Column	Column_alias	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
-def					t	253	7	7	Y	0	31	8
+def					t	253	7	7	Y	0	39	8
 t
 1000000
 1      
@@ -2527,7 +2527,7 @@ create table t1(a float);
 insert into t1 values (1.33);
 select format(a, 2) from t1;
 Catalog	Database	Table	Table_alias	Column	Column_alias	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
-def					format(a, 2)	253	49	4	Y	0	31	8
+def					format(a, 2)	253	57	4	Y	0	39	8
 format(a, 2)
 1.33
 drop table t1;
@@ -2855,7 +2855,7 @@ CREATE TABLE t1 AS SELECT format(123,2,'no_NO');
 SHOW CREATE TABLE t1;
 Table	Create Table
 t1	CREATE TABLE `t1` (
-  `format(123,2,'no_NO')` varchar(37) NOT NULL
+  `format(123,2,'no_NO')` varchar(45) NOT NULL
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 SELECT * FROM t1;
 format(123,2,'no_NO')