Improvements to README and tests

[ptomato]

This consists of various fixes and improvements to the build instructions and tests that I came across when building for the first time. (Doesn't fix any specific issue number.) See the individual commit messages for more explanation, but here's a summary:

• Add steps to the build instructions in the README describing how to install the jsparser test dependencies and which environment variables need to be set
• Fixes for the static binding generator tests (they relied on being able to load Java system classes from an actual JAR file, which doesn't exist in recent Java versions)
• A fix for the AST parser tests taking a really long time to time out if they failed

No new tests; the changes are either in the documentation, in the tests themselves, or fixes that enable the tests to complete successfully on my machine.

[cla-bot[bot]]

Thank you for your pull request and welcome to our community. We require contributors to sign our Contributor License Agreement, and we don't seem to have you on file. In order for us to review and merge your code, please sign the CLA at https://www.nativescript.org/cla. CLA has not been signed by users: @ptomato. After signing the CLA, you can ask me to recheck this PR by posting @cla-bot check as a comment to the PR.

[ptomato]

Retargeted to the feature/v8-10.3.22-perf branch for now.

[ptomato]

Retargeted back to main.