CommonGramsFilter assumes all input tokens have a length of 1 [LUCENE-4983]

CommonGramsFilter set posLenAttribute to 2 for bi-grams, no matter the length of the input tokens. Here is an example seed that produces a failure:
```
[junit4:junit4] says Привет! Master seed: 3296009A5B3B7A05
[junit4:junit4] Executing 1 suite with 1 JVM.
[junit4:junit4]
[junit4:junit4] Started J0 PID(23946@RD-38).
[junit4:junit4] Suite: org.apache.lucene.analysis.core.TestRandomChains
[junit4:junit4] 2> TEST FAIL: useCharFilter=true text='apuqdgtr wjco mpc '
[junit4:junit4] 2> Exception from random analyzer:
[junit4:junit4] 2> charfilters=
[junit4:junit4] 2> org.apache.lucene.analysis.pattern.PatternReplaceCharFilter(a, , java.io.StringReader@699f982d)
[junit4:junit4] 2> org.apache.lucene.analysis.charfilter.HTMLStripCharFilter(org.apache.lucene.analysis.pattern.PatternReplaceCharFilter@6cbfe887, [])
[junit4:junit4] 2> tokenizer=
[junit4:junit4] 2> org.apache.lucene.analysis.core.LetterTokenizer(LUCENE_44, org.apache.lucene.util.AttributeSource$AttributeFactory$DefaultAttributeFactory@4fb3c3d9, org.apache.lucene.analysis.core.TestRandomChains$CheckThatYouDidntReadAnythingReaderWrapper@2b3b2ed8)
[junit4:junit4] 2> filters=
[junit4:junit4] 2> org.apache.lucene.analysis.util.ElisionFilter(org.apache.lucene.analysis.ValidatingTokenFilter@0, [iez])
[junit4:junit4] 2> org.apache.lucene.analysis.MockGraphTokenFilter(java.util.Random@3a807d14, org.apache.lucene.analysis.ValidatingTokenFilter@20)
[junit4:junit4] 2> org.apache.lucene.analysis.commongrams.CommonGramsFilter(LUCENE_44, org.apache.lucene.analysis.ValidatingTokenFilter@37caea, [bbtzjxco, , jafehvlp, kujsm, znpfw, xqfni])
[junit4:junit4] 2> org.apache.lucene.analysis.bg.BulgarianStemFilter(org.apache.lucene.analysis.ValidatingTokenFilter@6c1927b)
[junit4:junit4] 2> offsetsAreCorrect=true
[junit4:junit4] 2> NOTE: reproduce with: ant test -Dtestcase=TestRandomChains -Dtests.method=testRandomChains -Dtests.seed=3296009A5B3B7A05 -Dtests.multiplier=3 -Dtests.slow=true -Dtests.locale=ar_YE -Dtests.timezone=Europe/London -Dtests.file.encoding=US-ASCII
[junit4:junit4] ERROR 14.7s | TestRandomChains.testRandomChains <<<
[junit4:junit4] > Throwable #1: java.lang.IllegalStateException: stage 3: inconsistent endOffset at pos=2: 13 vs 8; token=￯[㑮ٯb_
[junit4:junit4] > at __randomizedtesting.SeedInfo.seed([3296009A5B3B7A05:F7729FB1C2967C5]:0)
[junit4:junit4] > at org.apache.lucene.analysis.ValidatingTokenFilter.incrementToken(ValidatingTokenFilter.java:135)
[junit4:junit4] > at org.apache.lucene.analysis.bg.BulgarianStemFilter.incrementToken(BulgarianStemFilter.java:48)
[junit4:junit4] > at org.apache.lucene.analysis.ValidatingTokenFilter.incrementToken(ValidatingTokenFilter.java:78)
[junit4:junit4] > at org.apache.lucene.analysis.BaseTokenStreamTestCase.checkAnalysisConsistency(BaseTokenStreamTestCase.java:635)
[junit4:junit4] > at org.apache.lucene.analysis.BaseTokenStreamTestCase.checkRandomData(BaseTokenStreamTestCase.java:546)
[junit4:junit4] > at org.apache.lucene.analysis.BaseTokenStreamTestCase.checkRandomData(BaseTokenStreamTestCase.java:447)
[junit4:junit4] > at org.apache.lucene.analysis.core.TestRandomChains.testRandomChains(TestRandomChains.java:944)
[junit4:junit4] > at java.lang.Thread.run(Thread.java:679)
[junit4:junit4] 2> NOTE: test params are: codec=Lucene42: {dummy=PostingsFormat(name=Direct)}, docValues:{}, sim=DefaultSimilarity, locale=ar_YE, timezone=Europe/London
[junit4:junit4] 2> NOTE: Linux 3.5.0-27-generic amd64/Sun Microsystems Inc. 1.6.0_27 (64-bit)/cpus=2,threads=1,free=96085824,total=223412224
[junit4:junit4] 2> NOTE: All tests run in this JVM: [TestRandomChains]
[junit4:junit4] Completed in 16.32s, 1 test, 1 error <<< FAILURES!
```

---
Migrated from [LUCENE-4983](https://issues.apache.org/jira/browse/LUCENE-4983) by Adrien Grand (@jpountz), updated Jan 05 2022
Linked issues:
- #5706

Start with CommonGramsFilter and reproduce the failure using TestRandomChains with the supplied ant test command and seed. Trace the position-length handling for bi-grams with variable-length input tokens, then verify that the supplied randomized test no longer reports the inconsistent endOffset failure.

Written by the indexing model from the issue text.