Fix assert false type parameter variables

[dicnunz]

Fixes #180

IssueHunt bounty: https://issuehunt.io/repos/71611551/issues/180

What changed

• Stop generating runtime variable type temporaries when both assertions and warnings are disabled.
• Add a regression fixture for a generic function with let bar: X and plugin option assert: false.

Why

With assert: false, assignment checks are disabled too, so the generated _barType = X temporary is unused. In generic functions it can reference a type parameter outside the runtime scope and produce undefined output.

Tested

• TEST_FILTER='180-assert-false-type-parameter' yarn --cwd packages/babel-plugin-flow-runtime test
• yarn --cwd packages/flow-config-parser build
• yarn --cwd packages/babel-plugin-flow-runtime build
• yarn --cwd packages/babel-plugin-flow-runtime test (239 passing)
• yarn --cwd packages/babel-plugin-flow-runtime lint (exits 0; existing repo-wide jsx-a11y rule warnings only)
• git diff --check

Note: full root yarn install --frozen-lockfile reaches dependency linking but fails while building an unrelated old docs node-sass dependency because node-gyp expects python/python2. I used a temporary GIT_CONFIG_GLOBAL rewrite for the old git://github.com dependency URL during install.

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IssueHunt Summary

Referenced issues

This pull request has been submitted to:

• #180: babel-plugin-flow-runtime references undefined type parameter names with assertions disabled

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