Export isDev const from solid-js/web

[thetarnav]

Export isDev const from solid-js/web to make checking development/production envs clearer than using the DEV object with internal methods.

Since the "_SOLID_DEV_" string was replaced with false only in production entries, I've enabled replacing in dev entries as well.
Otherwise, it would have to be declared this way:

export const isDev: boolean = !!"_SOLID_DEV_";

Which is tree shakeable too

[changeset-bot]

🦋 Changeset detected

Latest commit: 8a83011

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
solid-js	Patch
test-integration	Patch

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[coveralls]

Pull Request Test Coverage Report for Build 4256293149

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.004%) to 88.253%

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Files with Coverage Reduction	New Missed Lines	%
packages/solid/web/src/index.ts	2	82.19%

Totals
Change from base Build 4248345040:	0.004%
Covered Lines:	1301
Relevant Lines:	1398

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💛 - Coveralls