Add fraction_field_type and define fraction_field method for fields

[fingolfin]

Relanding PR #2092 (see also #2128 and #2130). Needs oscar-system/Oscar.jl#5153

[codecov]

Codecov Report

❌ Patch coverage is 81.48148% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.15%. Comparing base (02ad3a9) to head (0e64438).
⚠️ Report is 7 commits behind head on master.

Files with missing lines	Patch %	Lines
src/Fraction.jl	55.55%	4 Missing ⚠️
src/generic/RationalFunctionField.jl	94.11%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2132      +/-   ##
==========================================
+ Coverage   87.98%   88.15%   +0.17%     
==========================================
  Files         126      126              
  Lines       31665    32355     +690     
==========================================
+ Hits        27860    28524     +664     
- Misses       3805     3831      +26     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[lgoettgens]

Added a breaking label since this needs downstream changes in form of oscar-system/Oscar.jl#5153

[fingolfin]

Re-running CI now. Assuming this passes, I hope we can include it in the next breaking release.