Move steps in pull-shared-core.sh to language with proper regex support

[bschwedler]

The current process of creating a new SDK release process pulls in the shared_core library from the rstudio repo. Various modifications are made to these files using regexes and sed.

It would be beneficial to move this into a language that has full regex support as part of its standard library. This will allow modification of the files in memory as well as having the following additional benefits:

• Named match groups in regex patterns
• Multi-line regexes
• lookahead/lookbehind assertions
• Saving compiled regex to variables
• Combining already-defined regexes into more complex patterns

This should result in more flexibility as well as improved readability and maintainability.

[bschwedler]

I am partial to python's re module, which has support for all the previously mentioned benefits. While it is definitely more verbose than the regex support in perl or ruby I have personally found that because it is more explicit it can be easier to follow for newcomers to regexes.