This PR upgrades the version of closure compiler used to minify the AMP runtime to v20190513.

Highlights:

• Updated compiler.jar with a custom built version based on v20190513
  • Reverts two breaking changes in closure compiler code (one, two) (required until ES6 module support for "type-only import" like goog.requireType or TS import type google/closure-compiler#3041 is fixed)
• Updated compiler-and-tests.jar with a custom built version based on v20190513
  • Follows the steps outlined here
• Updated documentation for custom build changes in README.amp
• Updated runner.jar after fixing code and tests to be compatible with latest compiler code
• Fixed a few type check errors discovered by the new version
• Adopted the recently introduced @closurePrimitive annotations for assertion functions
• Removed the getAssertionFunctions() override in AmpCodingConvention.java

Future work: Dynamically generate runner.jar once we no longer need a custom built compiler.jar (#22452)

Companion to #22368
Partial fix for #18748
Follow up to #18552, #18609, #18794, #19449, #20056, and #21618