Fixes #1265. Support setting column widths

[robertpanzer]

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Kind of change

• Bug fix
• New non-breaking feature
• New breaking feature
• Documentation update
• Build improvement

Description

What is the goal of this pull request?

Add support for setting the width of table columns.
While columns have a method setWidth() that sets the attribute width of a column, this does not become effective.
In addition it is required to set the attribute colpcwidth, which Asciidoctor core only sets internally when calling Table#assign_column_widths.

How does it achieve that?

This PR adds a method Table.assignColumnWidths which calls the Ruby method mentioned above.

Are there any alternative ways to implement this?

Very likely.

Are there any implications of this pull request? Anything a user must know?

There should be no change of existing behavior.

Issue

If this PR fixes an open issue, please add a line of the form:

Fixes #1265

This PR is a draft until more tests, in particular for the auto width_cols are added.

Release notes

Please add a corresponding entry to the file CHANGELOG.adoc

[robertpanzer]

I added a test that uses autowidth columns, where the width attribute has a negative value.
Together with that I was considering adding an overloaded implementation for assignColumnWidths that allows to pass the widthBase.
Testing this I realized that I do not understand properly how this works, since the assigned widths were just the absolute widths set on the columns.
I.e., if I set the widths to 2, 3 and -1 for 3 columns, even with a width base of 10 the widths in the resulting html were 2, 3 and not set.
Therefore, I kept it like it is now, with only one implementation for assignColumnWidths.

[robertpanzer]

I can backport this to 2.5.x.