Change String growth to resize by 1.625x instead of 2x

[Catfish-Man]

Fixes rdar://59684914

[Catfish-Man]

@swift-ci please benchmark

[Catfish-Man]

WOO! That did the trick! No more magazine_malloc perf cliff.

16:43:51  ------- Performance (x86_64): -O -------
16:43:51  
16:43:51  REGRESSION                                    OLD       NEW        DELTA    RATIO    
16:43:51  UTF8Decode_InitFromData                       143.75    173.5      +20.7%   **0.83x (?)**
16:43:51  UTF8Decode_InitFromBytes                      162.5     194.0      +19.4%   **0.84x (?)**
16:43:51  StringComparison_ascii                        198.909   225.556    +13.4%   **0.88x (?)**
16:43:51  StringSwitch                                  275.143   310.833    +13.0%   **0.89x (?)**
16:43:51  SortStrings                                   482.75    531.5      +10.1%   **0.91x (?)**
16:43:51  Calculator                                    159.333   174.182    +9.3%    **0.91x (?)**
16:43:51  Breadcrumbs.CopyUTF16CodeUnits.Mixed          45.171    49.05      +8.6%    **0.92x (?)**
16:43:51  
16:43:51  IMPROVEMENT                                   OLD       NEW        DELTA    RATIO    
16:43:51  EqualStringSubstring                          29.6      22.038     -25.5%   **1.34x (?)**
16:43:51  Breadcrumbs.CopyAllUTF16CodeUnits.Mixed       203.545   153.0      -24.8%   **1.33x**
16:43:51  Breadcrumbs.CopyUTF16CodeUnits.longMixed      206.364   156.333    -24.2%   **1.32x (?)**
16:43:51  Breadcrumbs.CopyAllUTF16CodeUnits.longMixed   201.333   152.688    -24.2%   **1.32x**
16:43:51  EqualSubstringString                          29.719    22.604     -23.9%   **1.31x (?)**
16:43:51  Data.hash.Medium                              38.074    30.097     -21.0%   **1.27x (?)**
16:43:51  LessSubstringSubstring                        30.5      24.875     -18.4%   **1.23x (?)**
16:43:51  LessSubstringSubstringGenericComparable       30.483    25.029     -17.9%   **1.22x (?)**
16:43:51  EqualSubstringSubstringGenericEquatable       30.714    25.25      -17.8%   **1.22x (?)**
16:43:51  EqualSubstringSubstring                       30.04     25.34      -15.6%   **1.19x (?)**
16:43:51  StringDistance.utf16.ascii                    144.938   122.684    -15.4%   **1.18x (?)**
16:43:51  StringHashing_nonBMPSlowestPrenormal          500.256   431.395    -13.8%   **1.16x (?)**
16:43:51  NSString.bridged.byteCount.ascii.ascii        0.49      0.423      -13.6%   **1.16x (?)**
16:43:51  StringComparison_longSharedPrefix             228.091   205.0      -10.1%   **1.11x (?)**
16:43:51  SubstringEqualString                          158.636   142.727    -10.0%   **1.11x (?)**
16:43:51  StringHashing_emoji                           387.5     349.231    -9.9%    **1.11x (?)**
16:43:51  SubstringEquatable                            305.5     275.429    -9.8%    **1.11x (?)**
16:43:51  SubstringFromLongStringGeneric2               29.625    26.721     -9.8%    **1.11x (?)**
16:43:51  StringHashing_slowerPrenormal                 331.5     303.571    -8.4%    **1.09x (?)**
16:43:51  StringHasPrefixAscii                          2455.0    2251.111   -8.3%    **1.09x (?)**
16:43:51  StringHasSuffixUnicode                        52120.0   48000.0    -7.9%    **1.09x (?)**
16:43:51  SortStringsUnicode                            2330.0    2149.0     -7.8%    **1.08x (?)**
16:43:51  ObjectiveCBridgeStringHash                    63.552    59.032     -7.1%    **1.08x (?)**
16:43:51  StringHashing_latin1                          196.19    182.385    -7.0%    **1.08x (?)**
16:43:51  UTF8Decode_InitFromCustom_contiguous_ascii    176.643   164.917    -6.6%    **1.07x (?)**

[Catfish-Man]

@swift-ci please test

[Catfish-Man]

@swift-ci please test