[6.x] Float database types fix

[mnabialek]

At the moment it's impossible to change unsigned float/decimal columns to signed using Laravel Blueprint methods. This change fixes the problem

This is alternative implementation to #30890 where signature of methods was updated.

For consitency same change was done for double however it's impossible to update double colum out of the box using doctribe/dbal.

Proof of problem:

1st migration:

Schema::create('users', function (Blueprint $table) {
    $table->bigIncrements('id');
    $table->integer('a')->unsigned();
    $table->float('b')->unsigned();
    $table->decimal('d')->unsigned();
});

2nd migration:

Schema::table('users', function (Blueprint $table) {
    $table->integer('a')->change();
    $table->float('b')->change();
    $table->decimal('d')->change();
});

Run first migration and then run migrate --pretend as a result you get:

ALTER TABLE users CHANGE a a INT NOT NULL, CHANGE b b DOUBLE PRECISION UNSIGNED NOT NULL, CHANGE d d NUMERIC(8, 2) UNSIGNED NOT NULL

As you see integer column was changed to signed, however float and decimal weren't. After fix result of this is:

ALTER TABLE users CHANGE a a INT NOT NULL, CHANGE b b DOUBLE PRECISION NOT NULL, CHANGE d d NUMERIC(8, 2) NOT NULL

as expected.

[GrahamCampbell]

Thanks for the PR. I think this would probably have to go to 7.x, instead of 6.x, since it's a breaking change.

[mnabialek]

Is it not a bug fix? When we have columns in database and don't use unsigned when altering them they should not be unsigned anymore.