Use camel case for parameter names in ibm_db2.stub.php

[phansys]

The parameter $colnum in db2_lob_read() was also renamed to $columnNumber;

TODO:

• Wait for Update ibm_db2.stub.php #32.

[tessus]

I think we always used underscores in ibmdb2. But in reality it doesn't matter as long as it is consistent. I defer judgement to the devs who took this over.

[phansys]

I understand. I'm proposing this change because I saw the camel case as the most used style in modern PHP libraries. Also, it is already used in other extensions (like PDO, by instance).
By other hand, the casing is actually different between the base (English) documentation and other translations:

• EN: https://github.com/php/doc-en/blob/38785e987736461dd63952c887e2079a83187ba4/reference/ibm_db2/functions/db2-bind-param.xml#L16 (camel case);
• ES: https://github.com/php/doc-es/blob/d520c68797f6f3feb82746a191ffa2a645ae21cb/reference/ibm_db2/functions/db2-bind-param.xml#L17 (kebab case).

[NattyNarwhal]

I'm also fine with doing whatever as long as it's consistent.

[phansys]

I decided to close this PR by now, as I confirmed that the stub generates the proper documentation using underscores. The lack of consistency between translations seems to be a human mistake.
Given that there are many tools relying on the names of the current parameters, I think there is no great gain with this change.

Thank you!