fix(non linear font scaling): fix tests polluting the cache

The allFeasibleScalesAndConversionsDoNotCrash() test puts like every
possible value into the cache, which causes
missingLookupTable_cachesInterpolated() to find a value where it's not
expecting one.

Thus we restore the original default values at the end of every test.

Also fix the test tolerance to be larger.

Fix: 316968558
Fix: 317159831
Test: atest FontScaleConverterFactoryTest
Flag: N/A

Change-Id: I2117a22fdf985af69a02a91ecf490d98c3c865c6