DBAL-404: Support of index length for text fields

[doctrinebot]

Jira issue originally created by user maxlun86:

For table with text field description with index on it generated query is:

CREATE TABLE t (id INT UNSIGNED AUTO_INCREMENT NOT NULL, description LONGTEXT DEFAULT NULL, number INT DEFAULT NULL, INDEX index2 (description), INDEX index3 (description, number), PRIMARY KEY(id)) DEFAULT CHARACTER SET utf8 COLLATE utf8_unicode_ci ENGINE = InnoDB

This query lead to error, because for index on text field absented key length.

[github-actions]

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