Fix header area blob controls missing blobPath route check

Yousef Mahmoudrequested to merge
gitlab-community/gitlab-org/gitlab:630944-header-area-blob-path-route-check into master

What does this MR do and why?

Fix header area blob controls missing blobPath route check.

The isTreeView and showBlobControls computed properties in header_area.vue only checked for blobPathDecoded and blobPathEncoded route names, missing the blobPath route. This caused blob controls to not render and the tree view to incorrectly activate when navigating to a file via the blobPath route.

Related to #630944 (closed)

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