Remove direct dependence between fm2js/ and third_party/icu

The remainder of the codebase calls through fx_extension.h to
get this functionality, so fm2js should do the same.

Change-Id: I1f92b1b5138863a225c2c6efd325b603de3e50b4
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/63950
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>

xfa/fxfa/fm2js/BUILD.gn

diff --git a/xfa/fxfa/fm2js/BUILD.gn b/xfa/fxfa/fm2js/BUILD.gn
index ff33e10..7782b39 100644
--- a/xfa/fxfa/fm2js/BUILD.gn
+++ b/xfa/fxfa/fm2js/BUILD.gn
@@ -22,7 +22,6 @@
   ]
   deps = [
     "../../../core/fxcrt",
-    "//third_party/icu:icuuc",
   ]
   configs += [
     "../../../:pdfium_core_config",

xfa/fxfa/fm2js/cxfa_fmlexer.cpp

diff --git a/xfa/fxfa/fm2js/cxfa_fmlexer.cpp b/xfa/fxfa/fm2js/cxfa_fmlexer.cpp
index 11157a2..efb59f2 100644
--- a/xfa/fxfa/fm2js/cxfa_fmlexer.cpp
+++ b/xfa/fxfa/fm2js/cxfa_fmlexer.cpp
@@ -9,7 +9,6 @@
 #include <algorithm>
 
 #include "core/fxcrt/fx_extension.h"
-#include "third_party/icu/source/common/unicode/uchar.h"
 
 namespace {
 
@@ -19,14 +18,14 @@
 }
 
 bool IsIdentifierCharacter(wchar_t c) {
-  return u_isalnum(c) || c == 0x005F ||  // '_'
-         c == 0x0024;                    // '$'
+  return FXSYS_iswalnum(c) || c == 0x005F ||  // '_'
+         c == 0x0024;                         // '$'
 }
 
 bool IsInitialIdentifierCharacter(wchar_t c) {
-  return u_isalpha(c) || c == 0x005F ||  // '_'
-         c == 0x0024 ||                  // '$'
-         c == 0x0021;                    // '!'
+  return FXSYS_iswalpha(c) || c == 0x005F ||  // '_'
+         c == 0x0024 ||                       // '$'
+         c == 0x0021;                         // '!'
 }
 
 bool IsWhitespaceCharacter(wchar_t c) {