signed value not extended to 64 bits before assigning to register for arm64 `ldrsw`

[xxr0ss]

Version and Platform (required):

• Binary Ninja Version: 5.1.8104 Personal, 6eaaf348
• OS: windows
• OS Version: 11
• CPU Architecture: x86_64

Bug Description:
arm64 LDRSW <Xt>, <label>, according to Arm Architecture Reference Manual, does sign extension to 64 bits

but BN doesn't assign 64 bits negative value to the register, causing control flow analysis of indirect jump wrong in this case.

Steps To Reproduce:
load the attachment at 0x83af8, using aarch64

Expected Behavior:

• ldrsw x6, data_83b50 sets x6=0xffffffffffffff4c instead of 0xffffff4c
• br x25 jumps to 0x83b64 instead of 0x100083b64

Screenshots:

Binary:

binary_0x83af8_0x84.txt

[yrp604]

Should be fixed on dev: #7296

[xxr0ss]

Should be fixed on dev: #7296

oh, exactly