Move leap seconds DateTime configuration statics into LeapSecondCache

[jkotas]

This enables AOT initialization of public readonly DateTime statics like DateTime.Min/MaxValue.

[ghost]

I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label.

[jkotas]

Context: #77102 (comment)

[EgorBo]

Thanks, validate locally with changes from #77102 that this:

static bool Test(DateTime dt) => dt == DateTime.MinValue;

Emits:

; Assembly listing for method Program:Test(System.DateTime):bool
; Emitting BLENDED_CODE for X64 CPU with SSE2 - Windows
; ReadyToRun compilation
; optimized code
; rsp based frame
; partially interruptible
; Final local variable assignments
;
;* V00 arg0         [V00    ] (  0,  0   )  struct ( 8) zero-ref    single-def
;# V01 OutArgs      [V01    ] (  1,  1   )  lclBlk ( 0) [rsp+00H]   "OutgoingArgSpace"
;* V02 tmp1         [V02    ] (  0,  0   )  struct ( 8) zero-ref    "folding static ro fld struct"
;* V03 tmp2         [V03    ] (  0,  0   )  struct ( 8) zero-ref    "Inlining Arg"
;* V04 tmp3         [V04    ] (  0,  0   )  struct ( 8) zero-ref    "Inlining Arg"
;  V05 tmp4         [V05,T00] (  2,  2   )    long  ->  rcx         single-def V00._dateData(offs=0x00) P-INDEP "field V00._dateData (fldOffset=0x0)"
;* V06 tmp5         [V06    ] (  0,  0   )    long  ->  zero-ref    V02._dateData(offs=0x00) P-INDEP "field V02._dateData (fldOffset=0x0)"
;* V07 tmp6         [V07    ] (  0,  0   )    long  ->  zero-ref    V03._dateData(offs=0x00) P-INDEP "field V03._dateData (fldOffset=0x0)"
;* V08 tmp7         [V08    ] (  0,  0   )    long  ->  zero-ref    V04._dateData(offs=0x00) P-INDEP "field V04._dateData (fldOffset=0x0)"
;
; Lcl frame size = 0

G_M44292_IG01:              ;; offset=0000H
						;; size=0 bbWeight=1    PerfScore 0.00
G_M44292_IG02:              ;; offset=0000H
       48C1E102             shl      rcx, 2
       0F94C0               sete     al
       0FB6C0               movzx    rax, al
						;; size=10 bbWeight=1    PerfScore 1.75
G_M44292_IG03:              ;; offset=000AH
       C3                   ret      
						;; size=1 bbWeight=1    PerfScore 1.00

; Total bytes of code 11, prolog size 0, PerfScore 3.85, instruction count 4, allocated bytes for code 11 (MethodHash=313f52fb) for method Program:Test(System.DateTime):bool
; ============================================================

on NativeAOT