i18n: reduce unnecessary message formats

[brendankenny]

alternate approach to memoization in #14026

Memoization needs to be on the icuMessageFn and the ICU replacement values, since messages with different replacements are going to end up different as different strings in the end. One way to avoid the extra arg bookkeeping work would be to memoize only strings with no replacements, which is most of the strings (especially during config generation, where it's mostly checking audit title, failureTitle, description, etc.

The root performance problem is that IntlMessageFormat is relatively slow, and we call it a lot. If you look at a profile, it's spending almost all its time parsing each message (which to be fair, is apparently much faster in more recent intl-messageformat versions and I'm the one who has resisted updating).

Since ICU placeholders have to occur inside {}, and most of our strings don't have any replacements, this PR instead adds a simple filter that just checks if the message has a { in it before attempting to parse it. This will catch all messages with placeholders (letting in false positives with escaped { in them, but I don't believe we have any right now?). The result is equivalent to the "memoize only strings with no replacements" mentioned above.

This is slightly less efficient than memoizing the whole thing, but almost all formatted strings have no placeholders, and of those that do, only a fraction will have repeated placeholder replacements that would get a cache hit.

75 out of 880 messages (8.5%) in en-US.json have ICU placeholders in them, but almost all of those are things like displayValues and the like, which are used rarely. In a real run using the command in #14026

node ./lighthouse-cli --quiet -A=./lighthouse-core/test/results/artifacts --config-path=./lighthouse-core/test/results/sample-config.js --output=json --output-path=./lighthouse-core/test/results/sample_v2.json

of the 16,608 messages that pass through getIcuMessageFn, 42 (0.25%) need a replacement, so it's probably not worth the extra effort for them.

---

results of

node ./lighthouse-cli --quiet -A=./lighthouse-core/test/results/artifacts --config-path=./lighthouse-core/test/results/sample-config.js --output=json --output-path=./lighthouse-core/test/results/sample_v2.json; 
node -e "t = require('./lighthouse-core/test/results/sample_v2.json'); console.log(t.timing.entries.filter(e => e.name === 'lh:config').at(-1).duration)"

# this branch
376.38
176.09
170.07
181.17
189.9

# master
541.81
522.81
497.86
538.26
512.19

which look roughly equivalent to the #14026 improvements to me

[brendankenny]

also requires that values is undefined so it preserves the behavior of throwing on invalid values for messages with no placeholders

[paulirish]

simpler! i dig it.