Add ParagraphStyle setting to choose whether missing font weight/slant should be faked

[samizdatco]

Motivation

OneLineShaper currently compares each typeface to the requested FontStyle and detects cases where there is a mismatch in terms of italic/upright-ness or bold-ness (with a threshold of semibold or heavier counting as 'bold'). If it detects a mismatch it will apply a shear transform to create a fake italic or outdent the strokes to create a fake bold.

While there are cases where this automated behavior is desirable, there are also times where it is preferable to use an unmodified typeface (albeit with a different style than requested) rather than a synthetically generated one.

Changes

This PR adds a boolean property to ParagraphStyle called fFakeMissingFontStyles which defaults to true (so as not to change the current default behavior) but can be toggled to false by calling the setFakeMissingFontStyles() accessor. OneLineShaper has been updated to apply its faking routines only if the flag is enabled.

[skia-codereview-bot]

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