fix: do not skip a function body inside a template substitution

[marevol]

Stacked on #52.

A function body inside a substitution parsed fine but exploded the moment the function around it was called:

function outer() { return `${ (function () { return 7; })() }`; }
print(outer());
// ParserException: Missing close quote

Defining outer was enough to be fine; only invoking it failed, so this was the on-demand re-parse rather than the first parse.

Cause

When the parser skips a nested function body it restarts the lexer at the body's closing brace. A lexer started there has no template state, so the brace that ends the substitution is read as an ordinary one and the closing quote is read as opening a new template, which then runs to the end of the file.

Handing the state to the restarted lexer is not enough to fix it. The state has to be the state at that brace, and the lexer has read ahead by then — the same reason position and line are taken from the token rather than from the lexer. The lexer is typically past the whole template by then and reports no open substitution at all.

Fix

The body is not skipped there. skipFunctionBody already declines in two other cases and its caller is written for that: it parses the body and throws it away. A substitution is a small enough place that giving up the skip costs little, and the nested function is still compiled on demand in its own right — its source range is its own text, with no template around it.

Also covered: an object-literal method, a brace-bodied arrow, two bodies in one substitution, a nested template, and braces within the body.

Verification

./gradlew build testOptimistic testPessimistic

suite	before	after
test	665, 0 fail	665, 0 fail
testOptimistic	1715, 0 fail	1715, 0 fail
testPessimistic	1715, 0 fail	1715, 0 fail