SNOW-802269 Add regextract signum subindex collectlist functions

[sfc-gh-sjayabalan]

• Added regexp_extract,signum,substring_index,collect_list

1) Added regexp_extract,signum,substring_index,collect_list to functions.scala . 2) Added test cases for the same

• Added examples and updated the description

• Fixed format

• formatted the comments

• Added java functions and unit test cases for java

• Added sign function

• Modified the alignment

• Added examples

• adjusted comments

• Update Functions.java

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   Fixes #NNNN

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[sfc-gh-bli]

Can you give it meaningful title? for example Add regextract, signum, subindex, and collectlist functions

BTW, please reformat your code by mvn clean compile. all merging gates failed.

[sfc-gh-sjayabalan]

Can you give it meaningful title? for example Add regextract, signum, subindex, and collectlist functions

BTW, please reformat your code by mvn clean compile. all merging gates failed.

• I did clean compile.Could you please validate