AST analyzer and assemblies split

[MikhailArkhipov]

Fixes #426
Fixes #408
Fixes #473

Base of of #406

Microsoft.Python.Core - common objects usable in many places
Microsoft.Python.Parsing - Python parser and AST
Microsoft.Python.Analysis.Engine - current DDG analysis
Microsoft.Python.Analysis.Core - dependency resolution and other code common to DDG and AST.
Microsoft.Python.Analysis - AST analysis

• No logic changes in DDG analysis apart from minor changes in references due to parser and core utilities relocation.

AST analysis:

• New test assembly with 92 tests
• Updated fluent assertions in the new test assembly
• Asynchronous document loading and analysis
• Asynchronous imports
• Asynchronous AST walk
• Removed lazy types
• Removed 'multiple types' constructs
• Stub is imported first
• Functions are not analyzed if stub equivalent is present. Instead, overload instance from the stub is used.
• Partial transfer of DDG functionality (Transfer type determination parts from DDG walker to AST walker #407).

[jakebailey]

Running the tests before approving this:

• ListCallCtor fails: Expected Type.TypeId to be Int, but found Unknown.
• Many of the parsing tests fail
  • MutateStdLib gives things like: Assert.AreEqual failed. Expected:<5>. Actual:<4>.
  • Most roundtrip tests fail, like: Assert.AreEqual failed. Expected:<*>. Actual:< >. Characters differ at 21, got , expected *

[jakebailey]

Alright, the tests seem to pass now, other than the FullStdLibAnaconda3 scrape test timing out. Building/running the old language server works as well.

[jakebailey]

I guess now is better than never. A lot of the in-progress items will probably need to be closed after this is merged.