fix: Fix for ReferenceError: pattern is not defined

[harmony7]

This PR fixes the following error thrown by the compiler when import-ing certain libraries:

> build
> js-compute-runtime bin/index.js bin/main.wasm

file:///Users/komuro/Developer/my-app/node_modules/@fastly/js-compute/src/precompile.js:37
        transpiledPattern = pattern;
        ^

ReferenceError: pattern is not defined
    at Literal (file:///Users/komuro/Developer/my-app/node_modules/@fastly/js-compute/src/precompile.js:37:9)
    at c (file:///Users/komuro/Developer/my-app/node_modules/acorn-walk/dist/walk.mjs:24:18)
    at Object.skipThrough (file:///Users/komuro/Developer/my-app/node_modules/acorn-walk/dist/walk.mjs:180:37)
    at c (file:///Users/komuro/Developer/my-app/node_modules/acorn-walk/dist/walk.mjs:23:22)
    at base.ArrayExpression (file:///Users/komuro/Developer/my-app/node_modules/acorn-walk/dist/walk.mjs:330:16)
    at c (file:///Users/komuro/Developer/my-app/node_modules/acorn-walk/dist/walk.mjs:23:22)
    at Object.skipThrough (file:///Users/komuro/Developer/my-app/node_modules/acorn-walk/dist/walk.mjs:180:37)
    at c (file:///Users/komuro/Developer/my-app/node_modules/acorn-walk/dist/walk.mjs:23:22)
    at base.ArrayExpression (file:///Users/komuro/Developer/my-app/node_modules/acorn-walk/dist/walk.mjs:330:16)
    at c (file:///Users/komuro/Developer/my-app/node_modules/acorn-walk/dist/walk.mjs:23:22)

Node.js v18.6.0
--------------------------------------------------------------------------------

✗ Running [scripts.build]

ERROR: error during execution process (see 'command output' above): exit status 1.

Some time between 1.7 and 1.8 changes were made to use acorn to walk code during src/precompile.js in processing regular expressions. Some of the worker code during the walking was modified, from

js-compute-runtime/src/precompile.js

Lines 16 to 26 in 8f38980

	const pattern = m.captures[0].node.text;
	const flags = m.captures[1]?.node.text || "";
	// transpile unicode property escapes
	let patternTranspiled;
	try {
	patternTranspiled = regexpuc(pattern, flags, { unicodePropertyEscapes: 'transform' });
	} catch {
	// swallow regex parse errors here to instead throw them at the engine level
	// this then also avoids regex parser bugs being thrown unnecessarily
	patternTranspiled = pattern;
	}

to

js-compute-runtime/src/precompile.js

Lines 28 to 38 in e3f4bdd

	if (!node.regex) return;
	let transpiledPattern;
	try {
	transpiledPattern = regexpuc(node.regex.pattern, node.regex.flags, {
	unicodePropertyEscapes: "transform",
	});
	} catch {
	// swallow regex parse errors here to instead throw them at the engine level
	// this then also avoids regex parser bugs being thrown unnecessarily
	transpiledPattern = pattern;
	}

When this was done, it looks like pattern in the catch block had not also been updated to node.regex.pattern.
This results in the error ReferenceError: pattern is not defined, as an identifier named pattern does not exist in scope.

This PR fixes this error.