CodexModule: Fix double-flipping in RTL

CodexModule::processStyle() looks at the path of the style file to
detect whether it's an already-flipped Codex file. In
I11c6a81a1ba34fe10f4b1c98bf76f0db40c1ce98 we broke this logic so that it
was comparing a full path (prefixed with MW_INSTALL_PATH) to a relative
path (not prefixed), so the detection always failed and we'd flip every
file. For Codex files, this meant we double-flipped the RTL files back
to LTR.

Follow-Up: I11c6a81a1ba34fe10f4b1c98bf76f0db40c1ce98
Bug: T373676
Change-Id: I49f14dcc503a3279362559197f12b2852276fb5e