Adds Ion 1.1 system symbols

[popematt]

Issue #, if available:

None.

Description of changes:

This adds an implementation of Ion 1.1 Symbols. Rather than try to kludge them into the existing SymbolToken interface, my plan is to treat them like a special case of symbols with inline text.

Also updates OpCode 0xEE to mean "system symbol" so that we're not sharing EF between system symbols and system macros because that was unnecessarily complicated to implement, and we didn't know if it was going to be a macro or a symbol until we read the second byte.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

Attention: Patch coverage is 11.90476% with 74 lines in your changes missing coverage. Please review.

Please upload report for BASE (ion-11-encoding@047e37a). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
...main/java/com/amazon/ion/impl/SystemSymbols_1_1.kt	0.00%	73 Missing ⚠️
src/main/java/com/amazon/ion/impl/IonTypeID.java	87.50%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@                Coverage Diff                 @@
##             ion-11-encoding     #939   +/-   ##
==================================================
  Coverage                   ?   69.82%           
  Complexity                 ?     6798           
==================================================
  Files                      ?      194           
  Lines                      ?    26955           
  Branches                   ?     4882           
==================================================
  Hits                       ?    18821           
  Misses                     ?     6635           
  Partials                   ?     1499           

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[zslayton]

LGTM! Some superficial comments to consider before merging below.