[FLINK-24908][Table SQL/Client] Improve SQL Error description for SQL Client

[snuyanzin]

What is the purpose of the change

There are some problem queries with misprints like

ELECT  1;
/*
comment
*/ SEECT 1;

Currently SQL client responses for such queries like Non-query expression encountered in illegal context. For larger queries it could be a time consuming task to understand what is wrong.

The PR is aimed to provide more info for such queries like exact unknown token and start position. So it will help to faster detect issues. In fact this info is already present in SqlParseException in pos field.

Brief change log

In case of SqlParseException and message Non-query expression encountered in illegal context extract and show pos info

Verifying this change

There are tests added to flink-table/flink-sql-client/src/test/resources/sql/select.q

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

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Automated Checks

Last check on commit e0da32f (Fri Nov 26 08:02:13 UTC 2021)

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