In Pg and Sqlite3, `:text` and `:binary` have variable unlimited length.
But in MySQL, these have limited length for each types (ref #21591, #21619).
This change adds short-hand methods for each text and blob types.

Example:

    create_table :foos do |t|
      t.tinyblob   :tiny_blob
      t.mediumblob :medium_blob
      t.longblob   :long_blob
      t.tinytext   :tiny_text
      t.mediumtext :medium_text
      t.longtext   :long_text
    end

Currently `tinyblob` is dumped to `t.binary "tiny_blob", limit: 255`.
But `t.binary ... limit: 255` is generating SQL to `varchar(255)`.
It is incorrect. This commit fixes this problem.

Example:

    create_table :foos do |t|
      t.string :string_utf8_bin, charset: 'utf8', collation: 'utf8_bin'
      t.text   :text_ascii,      charset: 'ascii'
    end

We've replaced most querues using DROP TABLE in our tests already.
This patch replaces the last couple calls.

enum includes text or blob or ... hooked by wrong regex

Only use LOWER for mysql case insensitive uniqueness check when column has a case sensitive collation.

[#3204 state:committed]
Signed-off-by: NJeremy Kemper <jeremy@bitsweat.net>

Create mysql binary_fields table with latin1 character set as with utf8 all the limits would have to be divided by 3 to get the expected text types
Signed-off-by: NJeremy Kemper <jeremy@bitsweat.net>

Move adapter specific schema into their own files
Signed-off-by: NMichael Koziarski <michael@koziarski.com>