[FLINK-13783][table] Implement type inference for string functions

[twalthr]

What is the purpose of the change

Updates the expressions:

CHAR_LENGTH
LIKE
LOWER
LOWERCASE
UPPER
UPPERCASE
INIT_CAP
RPAD
LPAD
RTRIM
LTRIM
SUBSTRING
CONCAT
CONCAT_WS
SHA1
SHA2
SHA224
SHA256
SHA384
SHA512
REPEAT
REPLACE
TO_BASE64
FROM_BASE64
POSITION
MD5
REGEXP_EXTRACT
REGEXP_REPLACE
SIMILAR
TRIM

Brief change log

• Expressions updated
• Old planner expressions removed

Verifying this change

This change is already covered by existing tests.

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

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): yes
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn/Mesos, ZooKeeper: no
• The S3 file system connector: no

Documentation

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

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Automated Checks

Last check on commit e3197af (Thu Jun 11 07:15:14 UTC 2020)

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CI report:

• e3197af Azure: FAILURE

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[dawidwys]

LGTM

[dawidwys]

nit: add a comment //overflow