Make sure that the preview banner is shown when there is no web folder

[matteodepalo]

WHY are these changes introduced?

Fixes https://github.com/Shopify/internal-cli-foundations/issues/550

We weren't showing the footer with the preview url in dev if there was no web folder and only UI extensions

WHAT is this pull request doing?

This PR makes sure that the previewUrl is initialized outside the check for web or backend. Note that if we had function or theme extensions only, we would still not show the banner, but this is temporary while we're moving the instructions for both to the dev console.

How to test your changes?

• Delete the web folder in the fixture app
• Run dev
• A footer with the dev console URL should appear

Measuring impact

How do we know this change was effective? Please choose one:

• n/a - this doesn't need measurement, e.g. a linting rule or a bug-fix
• Existing analytics will cater for this addition
• PR includes analytics changes to measure impact

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've made sure that any changes to dev or deploy have been reflected in the internal flowchart.

[github-actions]

Benchmark report

The following table contains a summary of the startup time for all commands.

Status	Command	Baseline (avg)	Current (avg)	Diff
🟢	app build	875 ms	869 ms	-0.69 %
🟢	app deploy	1047.33 ms	1051 ms	0.35 %
🟢	app dev	1054.33 ms	1054.67 ms	0.03 %
🟢	app env pull	958 ms	967 ms	0.94 %
🟢	app env show	954.33 ms	980 ms	2.69 %
🟢	app generate extension	1027.33 ms	1011.67 ms	-1.52 %
🟢	app generate schema	989.67 ms	988.33 ms	-0.13 %
🟢	app info	961 ms	965 ms	0.42 %
🟢	app scaffold extension	1012.67 ms	1024.67 ms	1.18 %
🟢	app update-url	937 ms	941 ms	0.43 %
🟢	theme check	816.33 ms	823 ms	0.82 %
🟢	theme delete	921.33 ms	919 ms	-0.25 %
🟢	theme dev	914.67 ms	912 ms	-0.29 %
🟢	theme help-old	821.33 ms	815.67 ms	-0.69 %
🟢	theme info	853.67 ms	853 ms	-0.08 %
🟢	theme init	831.33 ms	833.67 ms	0.28 %
🟢	theme language-server	815.33 ms	817.33 ms	0.25 %
🟢	theme list	931 ms	910.67 ms	-2.18 %
🟢	theme open	927 ms	932.67 ms	0.61 %
🟢	theme package	859.67 ms	856 ms	-0.43 %
🟢	theme publish	925 ms	926.67 ms	0.18 %
🟢	theme pull	909.67 ms	923.33 ms	1.5 %
🟢	theme push	910.67 ms	915.67 ms	0.55 %
🟢	theme serve	917.67 ms	920.33 ms	0.29 %
🟢	theme share	916.67 ms	911 ms	-0.62 %
🟢	webhook trigger	912.67 ms	922.67 ms	1.1 %

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🟡	Statements	71.85% (+0.01% 🔼)	3843/5349
🟡	Branches	69.42%	1739/2505
🟡	Functions	70.17%	1002/1428
🟡	Lines	73.08% (+0.01% 🔼)	3665/5015

Test suite run success

971 tests passing in 500 suites.

Report generated by 🧪jest coverage report action from c729e47