Frozen IOUs should still be transferable to/from the issuer

[vlntb]

High Level Overview of Change

The freeze logic was incorrectly blocking IOU issuers from transacting with their own frozen currency. This violated the XRP Ledger protocol, which specifies that "Counterparties of the frozen issuer can still send and receive payments directly to and from the issuing address."

Context of Change

Three issues were fixed:

1. isFrozen() function was returning true for issuers checking their own currency during global freeze, causing the issuer to be treated as frozen. The early return prevented reaching the later issuer exemption check.
2. LoanBrokerCoverDeposit::preclaim() was using accountHolds() with FreezeHandling::fhZERO_IF_FROZEN for all accounts, including issuers. Since issuers don't have a "balance" of their own tokens (infinite issuance ability), the balance check would return 0 and fail with tecINSUFFICIENT_FUNDS.
3. VaultWithdraw::preclaim() had checkFrozen() calls that were always executed, even when the destination or submitter was the asset issuer. Now skips freeze checks when either the destination or submitter is the IOU issuer.

Type of Change

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Refactor (non-breaking change that only restructures code)
• [ ] Performance (increase or change in throughput and/or latency)
• [ ] Tests (you added tests for code that already exists, or your new feature included in this PR)
• [ ] Documentation update
• [ ] Chore (no impact to binary, e.g. .gitignore, formatting, dropping support for older tooling)
• [ ] Release

API Impact

• [ ] Public API: New feature (new methods and/or new fields)
• [ ] Public API: Breaking change (in general, breaking changes should only impact the next api_version)
• [ ] libxrpl change (any change that may affect libxrpl or dependents of libxrpl)
• [ ] Peer protocol change (must be backward compatible or bump the peer protocol version)

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 79.1%. Comparing base (0aa4eed) to head (8523f42).

Additional details and impacted files

@@                      Coverage Diff                       @@
##           ximinez/lending-XLS-66-ongoing   #6113   +/-   ##
==============================================================
  Coverage                            79.1%   79.1%           
==============================================================
  Files                                 839     839           
  Lines                               71385   71399   +14     
  Branches                             8317    8315    -2     
==============================================================
+ Hits                                56481   56497   +16     
+ Misses                              14904   14902    -2     

Files with missing lines	Coverage Δ
src/libxrpl/ledger/View.cpp	94.5% <100.0%> (+<0.1%)	:arrow_up:
src/xrpld/app/tx/detail/LoanBrokerCoverDeposit.cpp	95.0% <100.0%> (+0.2%)	:arrow_up:
src/xrpld/app/tx/detail/VaultWithdraw.cpp	99.2% <100.0%> (+0.1%)	:arrow_up:

... and 1 file with indirect coverage changes

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