Support string functions for new engine

[chloe-zh]

The string functions we are planning to support can be referring to MySQL Reference Manual. For cases about null and missing values as the arguments, typically returns missing value if there is missing value in argument, else returns null if there is null value in argument, refer to AsterixDB for more details.

Work for each function includes:

• Function implementation in parser and runtime (please include the java docs when necessary)
• Unit test of implementation
• Comparison test that runs against ODFE-SQL, H2 and SQLite
• Documentation of user manual in corresponding category. Override legacy doc for functions existed in the old engine.
• Examples with doctest

Example pull request: #713

Pending work includes: (click to check if the function is finished)

Highest Prioritized:

• like
• not like
• regexp
• substr
• substring
• upper
• lower
• trim
• ltrim
• rtrim

Medium:

• concat
• concat_ws
• length
• strcmp

Low:

• ascii
• bin
• bit_length
• char
• char_length
• character_length
• elt
• export_set
• field
• find_in_set
• format
• from_base64
• hex
• insert
• instr
• lcase
• left
• load_file
• locate
• lpad
• make_set
• match
• mid
• not_regexp
• oct
• octet_length
• ord
• position
• quote
• regexp_instr
• regexp_like
• regexp_replace
• regexp_substr
• repeat
• replace
• reverse
• right
• rlike
• rpad
• soundex
• sounds_like
• space
• substring_index
• to_base64
• ucase
• unhex
• weight_string

[dai-chen]

An old issue for DIV function support: #228