Adds reusable RawValueExpr::resolve method

[zslayton]

This PR contains no new features, just a refactor.

There are some complex generics around the RawValueExpr type (described in dev comments therein) that made writing a centralized, reusable resolve method difficult to express. I guess I'm older and wiser now, though, 'cause I managed to figure it out this time around.

Along with adding the resolve method, I removed two places where the same logic had been implemented.

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 86.95652% with 3 lines in your changes missing coverage. Please review.

Project coverage is 77.27%. Comparing base (f36249e) to head (93870d8).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/lazy/expanded/e_expression.rs	33.33%	0 Missing and 2 partials ⚠️
src/lazy/decoder.rs	93.75%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #854   +/-   ##
=======================================
  Coverage   77.26%   77.27%           
=======================================
  Files         135      135           
  Lines       33415    33408    -7     
  Branches    33415    33408    -7     
=======================================
- Hits        25819    25815    -4     
+ Misses       5654     5650    -4     
- Partials     1942     1943    +1     

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