Update docs for deprecate-integer-display-length=true

[dveeden]

What is changed, added or deleted? (Required)

Update the docs to follow the change in default value for deprecate-integer-display-length.

This follows the behavior in MySQL.

Integer types can be defined like int(10) or int(8) or int. People often misunderstand the meaning of the number that is specified here (e.g. the 10 and the 8 here). This does not change the capacity of the value that can be stored it only changes how it might be displayed.

See also https://dev.mysql.com/doc/refman/8.0/en/numeric-type-attributes.html and pingcap/tidb#56529

Important: This changes the documentation for the variable and updates the page describing numeric types. However this does NOT update the output that might have changed.

Output that changes based on this variable:

• SHOW CREATE TABLE
• DESCRIBE <table>, EXPLAIN <table> and SHOW COLUMNS FROM ...
• EXPLAIN...

Which TiDB version(s) do your changes apply to? (Required)

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What is the related PR or file link(s)?

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• Other reference link(s):

Don't merge before this PR has been merged
pingcap/tidb#56529

Do your changes match any of the following descriptions?

• Delete files
• Change aliases
• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

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[dveeden]

/hold

[dveeden]

/unhold