Validate constant expressions for global/offsets initialization

[gumb0]

More validation for number of instructions in const expr will be added in #377

I will squash test commits before merging.

[codecov]

Codecov Report

Merging #372 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #372   +/-   ##
=======================================
  Coverage   99.32%   99.33%           
=======================================
  Files          42       42           
  Lines       12834    12902   +68     
=======================================
+ Hits        12748    12816   +68     
  Misses         86       86           

[chfast]

This looks good, with two nits:

1. Once you move a test to validation_test.cpp in the same commit where functional change is. Other time this is done in two separate commits.
2. I'd rather use global.get, not global_get in comments and error messages.

[gumb0]

1. Once you move a test to validation_test.cpp in the same commit where functional change is. Other time this is done in two separate commits.

I made separate commits with the moves, now there're more test commits.

2. I'd rather use global.get, not global_get in comments and error messages.

Changed.

[axic]

Will review this later today.

[gumb0]

Rebased.

[gumb0]

Rebased.

[gumb0]

Reordered commits.

[axic]

Replaced by individual PRs.