Nitishsharma/adding localization

[nitishsharma25]

A successful pipeline build: https://msdata.visualstudio.com/Database%20Systems/_build?definitionId=24040

Adding tasks in gulp file:

1. generate_metadata: This generates metadata file containing all the strings marked for localization in src directory.
2. exporti18n: From the metadata file generated and package.nls.json file, this creates an XLF file containing all the strings marked for localization in the project. This XLF file is picked by translation pipeline. The translation pipeline returns XLF files for different languages in transXlf directory.
3. importi18n: It prepares json files in i18n directory for all languages from XLF files in transXlf dir.
4. addI18nTask: creates additional language files in i18n directory.
5. compile: normal compile, generates out directory.

[rishky-msft]

approving. As discussed with Nitish, will create separate PR for removing manual step in localization project.