parse and type-check optional modifiers in mapped types

[kevinbarabash]

TODO:

• [x] .d.ts codegen
• [x] handle T | undefined properly

[codecov[bot]]

Codecov Report

Merging #690 (4afb434) into main (621162b) will increase coverage by 0.33%. The diff coverage is 82.85%.

@@            Coverage Diff             @@
##             main     #690      +/-   ##
==========================================
+ Coverage   89.09%   89.42%   +0.33%     
==========================================
  Files         112      112              
  Lines       25173    25235      +62     
==========================================
+ Hits        22428    22567     +139     
+ Misses       2745     2668      -77     

Files Changed	Coverage Δ
crates/escalier_codegen/src/d_ts.rs	74.96% <44.44%> (+12.44%)	:arrow_up:
crates/escalier_hm/src/infer.rs	91.89% <85.71%> (-0.05%)	:arrow_down:
crates/escalier_interop/src/parse.rs	91.60% <88.88%> (-0.03%)	:arrow_down:
crates/escalier_ast/src/type_ann.rs	100.00% <100.00%> (ø)
crates/escalier_hm/src/folder.rs	87.20% <100.00%> (+0.09%)	:arrow_up:
crates/escalier_hm/src/types.rs	82.12% <100.00%> (+0.07%)	:arrow_up:
crates/escalier_hm/src/util.rs	80.33% <100.00%> (+0.24%)	:arrow_up:
crates/escalier_parser/src/type_ann_parser.rs	95.53% <100.00%> (+0.12%)	:arrow_up:

... and 3 files with indirect coverage changes