A plain text search should be performed when regex option is toggled off.

1. Search option should NOT perform a regex search when regex option is toggled off.
2. Regex searches are NOT being performed on queries that are already surrounded by forward slashes.

Problem with code:
Checks and edits during our const Query creation are too broad.

1. Queries were being surrounded by forward slashes even when they were already included in the query, eg below.
query = /example/ would then become //example//
2. In the try/catch where a new regex is created, regex.text('/example/') would create a regex for our query which is expected BUT should only occur when our Regex search option is enabled.

Fix:
Added additional checks during the creation of a new Regex.

1. First confirm this.isRegex is true && our query is NOT already surrounded by forward slashes before adding any.
2. Added an additional this.isRegex check on all new Regex creations.

R=szuend@chromium.org

Fixed: 349428386
Change-Id: If4a985c7cec3098f6a5358c9091db8b2cfe6890c
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/5683367
Reviewed-by: Simon Zünd <szuend@chromium.org>
Commit-Queue: Simon Zünd <szuend@chromium.org>